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A copy of the license -is included in the section entitled [[GNU Free Documentation -License|/fdl]]."]]"""]] - -[[!tag open_issue_glibc open_issue_libpthread]] - -[[!toc]] - - -# cthreads -> pthreads - -Get rid of cthreads; switch to pthreads. -Most of the issues raised on this page has been resolved, a few remain. - - -## IRC, freenode, #hurd, 2012-04-26 - - <pinotree> youpi: just to be sure: even if libpthread is compiled inside - glibc (with proper symbols forwarding etc), it doesn't change that you - cannot use both cthreads and pthreads in the same app, right? - -[[Packaging_libpthread]]. - - <youpi> it's the same libpthread - <youpi> symbol forwarding does not magically resolve that libpthread lacks - some libthread features :) - <pinotree> i know, i was referring about the clash between actively using - both - <youpi> there'll still be the issue that only one will be initialized - <youpi> and one that provides libc thread safety functions, etc. - <pinotree> that's what i wanted to knew, thanks :) - - -## IRC, freenode, #hurd, 2012-07-23 - - <bddebian> So I am not sure what to do with the hurd_condition_wait stuff - <braunr> i would also like to know what's the real issue with cancellation - here - <braunr> because my understanding is that libpthread already implements it - <braunr> does it look ok to you to make hurd_condition_timedwait return an - errno code (like ETIMEDOUT and ECANCELED) ? - <youpi> braunr: that's what pthread_* function usually do, yes - <braunr> i thought they used their own code - <youpi> no - <braunr> thanks - <braunr> well, first, do you understand what hurd_condition_wait is ? - <braunr> it's similar to condition_wait or pthread_cond_wait with a subtle - difference - <braunr> it differs from the original cthreads version by handling - cancellation - <braunr> but it also differs from the second by how it handles cancellation - <braunr> instead of calling registered cleanup routines and leaving, it - returns an error code - <braunr> (well simply !0 in this case) - <braunr> so there are two ways - <braunr> first, change the call to pthread_cond_wait - <bddebian> Are you saying we could fix stuff to use pthread_cond_wait() - properly? - <braunr> it's possible but not easy - <braunr> because you'd have to rewrite the cancellation code - <braunr> probably writing cleanup routines - <braunr> this can be hard and error prone - <braunr> and is useless if the code already exists - <braunr> so it seems reasonable to keep this hurd extension - <braunr> but now, as it *is* a hurd extension noone else uses - <antrik> braunr: BTW, when trying to figure out a tricky problem with the - auth server, cfhammer digged into the RPC cancellation code quite a bit, - and it's really a horrible complex monstrosity... plus the whole concept - is actually broken in some regards I think -- though I don't remember the - details - <braunr> antrik: i had the same kind of thoughts - <braunr> antrik: the hurd or pthreads ones ? - <antrik> not sure what you mean. I mean the RPC cancellation code -- which - is involves thread management too - <braunr> ok - <antrik> I don't know how it is related to hurd_condition_wait though - <braunr> well i found two main entry points there - <braunr> hurd_thread_cancel and hurd_condition_wait - <braunr> and it didn't look that bad - <braunr> whereas in the pthreads code, there are many corner cases - <braunr> and even the standard itself looks insane - <antrik> well, perhaps the threading part is not that bad... - <antrik> it's not where we saw the problems at any rate :-) - <braunr> rpc interruption maybe ? - <antrik> oh, right... interruption is probably the right term - <braunr> yes that thing looks scary - <braunr> :)) - <braunr> the migration thread paper mentions some things about the problems - concerning threads controllability - <antrik> I believe it's a very strong example for why building around - standard Mach features is a bad idea, instead of adapting the primitives - to our actual needs... - <braunr> i wouldn't be surprised if the "monstrosities" are work arounds - <braunr> right - - -## IRC, freenode, #hurd, 2012-07-26 - - <bddebian> Uhm, where does /usr/include/hurd/signal.h come from? - <pinotree> head -n4 /usr/include/hurd/signal. - <pinotree> h - <bddebian> Ohh glibc? - <bddebian> That makes things a little more difficult :( - <braunr> why ? - <bddebian> Hurd includes it which brings in cthreads - <braunr> ? - <braunr> the hurd already brings in cthreads - <braunr> i don't see what you mean - <bddebian> Not anymore :) - <braunr> the system cthreads header ? - <braunr> well it's not that difficult to trick the compiler not to include - them - <bddebian> signal.h includes cthreads.h I need to stop that - <braunr> just define the _CTHREADS_ macro before including anything - <braunr> remember that header files are normally enclosed in such macros to - avoid multiple inclusions - <braunr> this isn't specific to cthreads - <pinotree> converting hurd from cthreads to pthreads will make hurd and - glibc break source and binary compatibility - <bddebian> Of course - <braunr> reminds me of the similar issues of the late 90s - <bddebian> Ugh, why is he using _pthread_self()? - <pinotree> maybe because it accesses to the internals - <braunr> "he" ? - <bddebian> Thomas in his modified cancel-cond.c - <braunr> well, you need the internals to implement it - <braunr> hurd_condition_wait is similar to pthread_condition_wait, except - that instead of stopping the thread and calling cleanup routines, it - returns 1 if cancelled - <pinotree> not that i looked at it, but there's really no way to implement - it using public api? - <bddebian> Even if I am using glibc pthreads? - <braunr> unlikely - <bddebian> God I had all of this worked out before I dropped off for a - couple years.. :( - <braunr> this will come back :p - <pinotree> that makes you the perfect guy to work on it ;) - <bddebian> I can't find a pt-internal.h anywhere.. :( - <pinotree> clone the hurd/libpthread.git repo from savannah - <bddebian> Of course when I was doing this libpthread was still in hurd - sources... - <bddebian> So if I am using glibc pthread, why can't I use pthread_self() - instead? - <pinotree> that won't give you access to the internals - <bddebian> OK, dumb question time. What internals? - <pinotree> the libpthread ones - <braunr> that's where you will find if your thread has been cancelled or - not - <bddebian> pinotree: But isn't that assuming that I am using hurd's - libpthread? - <pinotree> if you aren't inside libpthread, no - <braunr> pthread_self is normally not portable - <braunr> you can only use it with pthread_equal - <braunr> so unless you *know* the internals, you can't use it - <braunr> and you won't be able to do much - <braunr> so, as it was done with cthreads, hurd_condition_wait should be - close to the libpthread implementation - <braunr> inside, normally - <braunr> now, if it's too long for you (i assume you don't want to build - glibc) - <braunr> you can just implement it outside, grabbing the internal headers - for now - <pinotree> another "not that i looked at it" question: isn't there no way - to rewrite the code using that custom condwait stuff to use the standard - libpthread one? - <braunr> and once it works, it'll get integrated - <braunr> pinotree: it looks very hard - <bddebian> braunr: But the internal headers are assuming hurd libpthread - which isn't in the source anymore - <braunr> from what i could see while working on select, servers very often - call hurd_condition_wait - <braunr> and they return EINTR if canceleld - <braunr> so if you use the standard pthread_cond_wait function, your thread - won't be able to return anything, unless you push the reply in a - completely separate callback - <braunr> i'm not sure how well mig can cope with that - <braunr> i'd say it can't :) - <braunr> no really it looks ugly - <braunr> it's far better to have this hurd specific function and keep the - existing user code as it is - <braunr> bddebian: you don't need the implementation, only the headers - <braunr> the thread, cond, mutex structures mostly - <bddebian> I should turn <pt-internal.h> to "pt-internal.h" and just put it - in libshouldbelibc, no? - <pinotree> no, that header is not installed - <bddebian> Obviously not the "best" way - <bddebian> pinotree: ?? - <braunr> pinotree: what does it change ? - <pinotree> braunr: it == ? - <braunr> bddebian: you could even copy it entirely in your new - cancel-cond.C and mention where it was copied from - <braunr> pinotree: it == pt-internal.H not being installed - <pinotree> that he cannot include it in libshouldbelibc sources? - <pinotree> ah, he wants to copy it? - <braunr> yes - <braunr> i want him to copy it actually :p - <braunr> it may be hard if there are a lot of macro options - <pinotree> the __pthread struct changes size and content depending on other - internal sysdeps headers - <braunr> well he needs to copy those too :p - <bddebian> Well even if this works we are going to have to do something - more "correct" about hurd_condition_wait. Maybe even putting it in - glibc? - <braunr> sure - <braunr> but again, don't waste time on this for now - <braunr> make it *work*, then it'll get integrated - <bddebian> Like it has already? This "patch" is only about 5 years old - now... ;-P - <braunr> but is it complete ? - <bddebian> Probably not :) - <bddebian> Hmm, I wonder how many undefined references I am going to get - though.. :( - <bddebian> Shit, 5 - <bddebian> One of which is ___pthread_self.. :( - <bddebian> Does that mean I am actually going to have to build hurds - libpthreads in libshouldbeinlibc? - <bddebian> Seriously, do I really need ___pthread_self, __pthread_self, - _pthread_self and pthread_self??? - <bddebian> I'm still unclear what to do with cancel-cond.c. It seems to me - that if I leave it the way it is currently I am going to have to either - re-add libpthreads or still all of the libpthreads code under - libshouldbeinlibc. - <braunr> then add it in libc - <braunr> glib - <braunr> glibc - <braunr> maybe under the name __hurd_condition_wait - <bddebian> Shouldn't I be able to interrupt cancel-cond stuff to use glibc - pthreads? - <braunr> interrupt ? - <bddebian> Meaning interject like they are doing. I may be missing the - point but they are just obfuscating libpthreads thread with some other - "namespace"? (I know my terminology is wrong, sorry). - <braunr> they ? - <bddebian> Well Thomas in this case but even in the old cthreads code, - whoever wrote cancel-cond.c - <braunr> but they use internal thread structures .. - <bddebian> Understood but at some level they are still just getting to a - libpthread thread, no? - <braunr> absolutely not .. - <braunr> there is *no* pthread stuff in the hurd - <braunr> that's the problem :p - <bddebian> Bah damnit... - <braunr> cthreads are directly implement on top of mach threads - <braunr> implemeneted* - <braunr> implemented* - <bddebian> Sure but hurd_condition_wait wasn't - <braunr> of course it is - <braunr> it's almost the same as condition_wait - <braunr> but returns 1 if a cancelation request was made - <bddebian> Grr, maybe I am just confusing myself because I am looking at - the modified (pthreads) version instead of the original cthreads version - of cancel-cond.c - <braunr> well if the modified version is fine, why not directly use that ? - <braunr> normally, hurd_condition_wait should sit next to other pthread - internal stuff - <braunr> it could be renamed __hurd_condition_wait, i'm not sure - <braunr> that's irrelevant for your work anyway - <bddebian> I am using it but it relies on libpthread and I am trying to use - glibc pthreads - <braunr> hum - <braunr> what's the difference between libpthread and "glibc pthreads" ? - <braunr> aren't glibc pthreads the merged libpthread ? - <bddebian> quite possibly but then I am missing something obvious. I'm - getting ___pthread_self in libshouldbeinlibc but it is *UND* - <braunr> bddebian: with unmodified binaries ? - <bddebian> braunr: No I added cancel-cond.c to libshouldbeinlibc - <bddebian> And some of the pt-xxx.h headers - <braunr> well it's normal then - <braunr> i suppose - <bddebian> braunr: So how do I get those defined without including - pthreads.c from libpthreads? :) - <antrik> pinotree: hm... I think we should try to make sure glibc works - both whith cthreads hurd and pthreads hurd. I hope that shoudn't be so - hard. - <antrik> breaking binary compatibility for the Hurd libs is not too - terrible I'd say -- as much as I'd like that, we do not exactly have a - lot of external stuff depending on them :-) - <braunr> bddebian: *sigh* - <braunr> bddebian: just add cancel-cond to glibc, near the pthread code :p - <bddebian> braunr: Wouldn't I still have the same issue? - <braunr> bddebian: what issue ? - <antrik> is hurd_condition_wait() the name of the original cthreads-based - function? - <braunr> antrik: the original is condition_wait - <antrik> I'm confused - <antrik> is condition_wait() a standard cthreads function, or a - Hurd-specific extension? - <braunr> antrik: as standard as you can get for something like cthreads - <bddebian> braunr: Where hurd_condition_wait is looking for "internals" as - you call them. I.E. there is no __pthread_self() in glibc pthreads :) - <braunr> hurd_condition_wait is the hurd-specific addition for cancelation - <braunr> bddebian: who cares ? - <braunr> bddebian: there is a pthread structure, and conditions, and - mutexes - <braunr> you need those definitions - <braunr> so you either import them in the hurd - <antrik> braunr: so hurd_condition_wait() *is* also used in the original - cthread-based implementation? - <braunr> or you write your code directly where they're available - <braunr> antrik: what do you call "original" ? - <antrik> not transitioned to pthreads - <braunr> ok, let's simply call that cthreads - <braunr> yes, it's used by every hurd servers - <braunr> virtually - <braunr> if not really everyone of them - <bddebian> braunr: That is where you are losing me. If I can just use - glibc pthreads structures, why can't I just use them in the new pthreads - version of cancel-cond.c which is what I was originally asking.. :) - <braunr> you *have* to do that - <braunr> but then, you have to build the whole glibc - * bddebian shoots himself - <braunr> and i was under the impression you wanted to avoid that - <antrik> do any standard pthread functions use identical names to any - standard cthread functions? - <braunr> what you *can't* do is use the standard pthreads interface - <braunr> no, not identical - <braunr> but very close - <braunr> bddebian: there is a difference between using pthreads, which - means using the standard posix interface, and using the glibc pthreads - structure, which means toying with the internale implementation - <braunr> you *cannot* implement hurd_condition_wait with the standard posix - interface, you need to use the internal structures - <braunr> hurd_condition_wait is actually a shurd specific addition to the - threading library - <braunr> hurd* - <antrik> well, in that case, the new pthread-based variant of - hurd_condition_wait() should also use a different name from the - cthread-based one - <braunr> so it's normal to put it in that threading library, like it was - done for cthreads - <braunr> 21:35 < braunr> it could be renamed __hurd_condition_wait, i'm not - sure - <bddebian> Except that I am trying to avoid using that threading library - <braunr> what ? - <bddebian> If I am understanding you correctly it is an extention to the - hurd specific libpthreads? - <braunr> to the threading library, whichever it is - <braunr> antrik: although, why not keeping the same name ? - <antrik> braunr: I don't think having hurd_condition_wait() for the cthread - variant and __hurd_condition_wait() would exactly help clarity... - <antrik> I was talking about a really new name. something like - pthread_hurd_condition_wait() or so - <antrik> braunr: to avoid confusion. to avoid accidentally pulling in the - wrong one at build and/or runtime. - <antrik> to avoid possible namespace conflicts - <braunr> ok - <braunr> well yes, makes sense - <bddebian> braunr: Let me state this as plainly as I hope I can. If I want - to use glibc's pthreads, I have no choice but to add it to glibc? - <braunr> and pthread_hurd_condition_wait is a fine name - <braunr> bddebian: no - <braunr> bddebian: you either add it there - <braunr> bddebian: or you copy the headers defining the internal structures - somewhere else and implement it there - <braunr> but adding it to glibc is better - <braunr> it's just longer in the beginning, and now i'm working on it, i'm - really not sure - <braunr> add it to glibc directly :p - <bddebian> That's what I am trying to do but the headers use pthread - specific stuff would should be coming from glibc's pthreads - <braunr> yes - <braunr> well it's not the headers you need - <braunr> you need the internal structure definitions - <braunr> sometimes they're in c files for opacity - <bddebian> So ___pthread_self() should eventually be an obfuscation of - glibcs pthread_self(), no? - <braunr> i don't know what it is - <braunr> read the cthreads variant of hurd_condition_wait, understand it, - do the same for pthreads - <braunr> it's easy :p - <bddebian> For you bastards that have a clue!! ;-P - <antrik> I definitely vote for adding it to the hurd pthreads - implementation in glibc right away. trying to do it externally only adds - unnecessary complications - <antrik> and we seem to agree that this new pthread function should be - named pthread_hurd_condition_wait(), not just hurd_condition_wait() :-) - - -## IRC, freenode, #hurd, 2012-07-27 - - <bddebian> OK this hurd_condition_wait stuff is getting ridiculous the way - I am trying to tackle it. :( I think I need a new tactic. - <braunr> bddebian: what do you mean ? - <bddebian> braunr: I know I am thick headed but I still don't get why I - cannot implement it in libshouldbeinlibc for now but still use glibc - pthreads internals - <bddebian> I thought I was getting close last night by bringing in all of - the hurd pthread headers and .c files but it just keeps getting uglier - and uglier - <bddebian> youpi: Just to verify. The /usr/lib/i386-gnu/libpthread.so that - ships with Debian now is from glibc, NOT libpthreads from Hurd right? - Everything I need should be available in glibc's libpthreads? (Except for - hurd_condition_wait obviously). - <braunr> 22:35 < antrik> I definitely vote for adding it to the hurd - pthreads implementation in glibc right away. trying to do it externally - only adds unnecessary complications - <youpi> bddebian: yes - <youpi> same as antrik - <bddebian> fuck - <youpi> libpthread *already* provides some odd symbols (cthread - compatibility), it can provide others - <braunr> bddebian: don't curse :p it will be easier in the long run - * bddebian breaks out glibc :( - <braunr> but you should tell thomas that too - <bddebian> braunr: I know it just adds a level of complexity that I may not - be able to deal with - <braunr> we wouldn't want him to waste too much time on the external - libpthread - <braunr> which one ? - <bddebian> glibc for one. hurd_condition_wait() for another which I don't - have a great grasp on. Remember my knowledge/skillsets are limited - currently. - <braunr> bddebian: tschwinge has good instructions to build glibc - <braunr> keep your tree around and it shouldn't be long to hack on it - <braunr> for hurd_condition_wait, i can help - <bddebian> Oh I was thinking about using Debian glibc for now. You think I - should do it from git? - <braunr> no - <braunr> debian rules are even more reliable - <braunr> (just don't build all the variants) - <pinotree> `debian/rules build_libc` builds the plain i386 variant only - <bddebian> So put pthread_hurd_cond_wait in it's own .c file or just put it - in pt-cond-wait.c ? - <braunr> i'd put it in pt-cond-wait.C - <bddebian> youpi or braunr: OK, another dumb question. What (if anything) - should I do about hurd/hurd/signal.h. Should I stop it from including - cthreads? - <youpi> it's not a dumb question. it should probably stop, yes, but there - might be uncovered issues, which we'll have to take care of - <bddebian> Well I know antrik suggested trying to keep compatibility but I - don't see how you would do that - <braunr> compability between what ? - <braunr> and source and/or binary ? - <youpi> hurd/signal.h implicitly including cthreads.h - <braunr> ah - <braunr> well yes, it has to change obviously - <bddebian> Which will break all the cthreads stuff of course - <bddebian> So are we agreeing on pthread_hurd_cond_wait()? - <braunr> that's fine - <bddebian> Ugh, shit there is stuff in glibc using cthreads?? - <braunr> like what ? - <bddebian> hurdsig, hurdsock, setauth, dtable, ... - <youpi> it's just using the compatibility stuff, that pthread does provide - <bddebian> but it includes cthreads.h implicitly - <bddebian> s/it/they in many cases - <youpi> not a problem, we provide the functions - <bddebian> Hmm, then what do I do about signal.h? It includes chtreads.h - because it uses extern struct mutex ... - <youpi> ah, then keep the include - <youpi> the pthread mutexes are compatible with that - <youpi> we'll clean that afterwards - <bddebian> arf, OK - <youpi> that's what I meant by "uncover issues" - - -## IRC, freenode, #hurd, 2012-07-28 - - <bddebian> Well crap, glibc built but I have no symbol for - pthread_hurd_cond_wait in libpthread.so :( - <bddebian> Hmm, I wonder if I have to add pthread_hurd_cond_wait to - forward.c and Versions? (Versions obviously eventually) - <pinotree> bddebian: most probably not about forward.c, but definitely you - have to export public stuff using Versions - - -## IRC, freenode, #hurd, 2012-07-29 - - <bddebian> braunr: http://paste.debian.net/181078/ - <braunr> ugh, inline functions :/ - <braunr> "Tell hurd_thread_cancel how to unblock us" - <braunr> i think you need that one too :p - <bddebian> ?? - <braunr> well, they work in pair - <braunr> one cancels, the other notices it - <braunr> hurd_thread_cancel is in the hurd though, iirc - <braunr> or uh wait - <braunr> no it's in glibc, hurd/thread-cancel.c - <braunr> otherwise it looks like a correct reuse of the original code, but - i need to understand the pthreads internals better to really say anything - - -## IRC, freenode, #hurd, 2012-08-03 - - <braunr> pinotree: what do you think of - condition_implies/condition_unimplies ? - <braunr> the work on pthread will have to replace those - - -## IRC, freenode, #hurd, 2012-08-06 - - <braunr> bddebian: so, where is the work being done ? - <bddebian> braunr: Right now I would just like to testing getting my glibc - with pthread_hurd_cond_wait installed on the clubber subhurd. It is in - /home/bdefreese/glibc-debian2 - <braunr> we need a git branch - <bddebian> braunr: Then I want to rebuild hurd with Thomas's pthread - patches against that new libc - <bddebian> Aye - <braunr> i don't remember, did thomas set a git repository somewhere for - that ? - <bddebian> He has one but I didn't have much luck with it since he is using - an external libpthreads - <braunr> i can manage the branches - <bddebian> I was actually patching debian/hurd then adding his patches on - top of that. It is in /home/bdefreese/debian-hurd but he has updateds - some stuff since then - <bddebian> Well we need to agree on a strategy. libpthreads only exists in - debian/glibc - <braunr> it would be better to have something upstream than to work on a - debian specific branch :/ - <braunr> tschwinge: do you think it can be done - <braunr> ? - - -## IRC, freenode, #hurd, 2012-08-07 - - <tschwinge> braunr: You mean to create on Savannah branches for the - libpthread conversion? Sure -- that's what I have been suggesting to - Barry and Thomas D. all the time. - - <bddebian> braunr: OK, so I installed my glibc with - pthread_hurd_condition_wait in the subhurd and now I have built Debian - Hurd with Thomas D's pthread patches. - <braunr> bddebian: i'm not sure we're ready for tests yet :p - <bddebian> braunr: Why not? :) - <braunr> bddebian: a few important bits are missing - <bddebian> braunr: Like? - <braunr> like condition_implies - <braunr> i'm not sure they have been handled everywhere - <braunr> it's still interesting to try, but i bet your system won't finish - booting - <bddebian> Well I haven't "installed" the built hurd yet - <bddebian> I was trying to think of a way to test a little bit first, like - maybe ext2fs.static or something - <bddebian> Ohh, it actually mounted the partition - <bddebian> How would I actually "test" it? - <braunr> git clone :p - <braunr> building a debian package inside - <braunr> removing the whole content after - <braunr> that sort of things - <bddebian> Hmm, I think I killed clubber :( - <bddebian> Yep.. Crap! :( - <braunr> ? - <braunr> how did you do that ? - <bddebian> Mounted a new partition with the pthreads ext2fs.static then did - an apt-get source hurd to it.. - <braunr> what partition, and what mount point ? - <bddebian> I added a new 2Gb partition on /dev/hd0s6 and set the translator - on /home/bdefreese/part6 - <braunr> shouldn't kill your hurd - <bddebian> Well it might still be up but killed my ssh session at the very - least :) - <braunr> ouch - <bddebian> braunr: Do you have debugging enabled in that custom kernel you - installed? Apparently it is sitting at the debug prompt. - - -## IRC, freenode, #hurd, 2012-08-12 - - <braunr> hmm, it seems the hurd notion of cancellation is actually not the - pthread one at all - <braunr> pthread_cancel merely marks a thread as being cancelled, while - hurd_thread_cancel interrupts it - <braunr> ok, i have a pthread_hurd_cond_wait_np function in glibc - - -## IRC, freenode, #hurd, 2012-08-13 - - <braunr> nice, i got ext2fs work with pthreads - <braunr> there are issues with the stack size strongly limiting the number - of concurrent threads, but that's easy to fix - <braunr> one problem with the hurd side is the condition implications - <braunr> i think it should be deal separately, and before doing anything - with pthreads - <braunr> but that's minor, the most complex part is, again, the term server - <braunr> other than that, it was pretty easy to do - <braunr> but, i shouldn't speak too soon, who knows what tricky bootstrap - issue i'm gonna face ;p - <braunr> tschwinge: i'd like to know how i should proceed if i want a - symbol in a library overriden by that of a main executable - <braunr> e.g. have libpthread define a default stack size, and let - executables define their own if they want to change it - <braunr> tschwinge: i suppose i should create a weak alias in the library - and a normal variable in the executable, right ? - <braunr> hm i'm making this too complicated - <braunr> don't mind that stupid question - <tschwinge> braunr: A simple variable definition would do, too, I think? - <tschwinge> braunr: Anyway, I'd first like to know why we can'T reduce the - size of libpthread threads from 2 MiB to 64 KiB as libthreads had. Is - that a requirement of the pthread specification? - <braunr> tschwinge: it's a requirement yes - <braunr> the main reason i see is that hurd threadvars (which are still - present) rely on common stack sizes and alignment to work - <tschwinge> Mhm, I see. - <braunr> so for now, i'm using this approach as a hack only - <tschwinge> I'm working on phasing out threadvars, but we're not there yet. - -[[glibc/t/tls-threadvar]]. - - <tschwinge> Yes, that's fine for the moment. - <braunr> tschwinge: a simple definition wouldn't work - <braunr> tschwinge: i resorted to a weak symbol, and see how it goes - <braunr> tschwinge: i supposed i need to export my symbol as a global one, - otherwise making it weak makes no sense, right ? - <braunr> suppose* - <braunr> tschwinge: also, i'm not actually sure what you meant is a - requirement about the stack size, i shouldn't have answered right away - <braunr> no there is actually no requirement - <braunr> i misunderstood your question - <braunr> hm when adding this weak variable, starting a program segfaults :( - <braunr> apparently on ___pthread_self, a tls variable - <braunr> fighting black magic begins - <braunr> arg, i can't manage to use that weak symbol to reduce stack sizes - :( - <braunr> ah yes, finally - <braunr> git clone /path/to/glibc.git on a pthread-powered ext2fs server :> - <braunr> tschwinge: seems i have problems using __thread in hurd code - <braunr> tschwinge: they produce undefined symbols - <braunr> tschwinge: forget that, another mistake on my part - <braunr> so, current state: i just need to create another patch, for the - code that is included in the debian hurd package but not in the upstream - hurd repository (e.g. procfs, netdde), and i should be able to create - hurd packages taht completely use pthreads - - -## IRC, freenode, #hurd, 2012-08-14 - - <braunr> tschwinge: i have weird bootstrap issues, as expected - <braunr> tschwinge: can you point me to important files involved during - bootstrap ? - <braunr> my ext2fs.static server refuses to start as a rootfs, whereas it - seems to work fine otherwise - <braunr> hm, it looks like it's related to global signal dispositions - - -## IRC, freenode, #hurd, 2012-08-15 - - <braunr> ahah, a subhurd running pthreads-powered hurd servers only - <LarstiQ> braunr: \o/ - <braunr> i can even long on ssh - <braunr> log - <braunr> pinotree: for reference, i uploaded my debian-specific changes - there : - <braunr> http://git.sceen.net/rbraun/debian_hurd.git/ - <braunr> darnassus is now running a pthreads-enabled hurd system :) - - -## IRC, freenode, #hurd, 2012-08-16 - - <braunr> my pthreads-enabled hurd systems can quickly die under load - <braunr> youpi: with hurd servers using pthreads, i occasionally see thread - storms apparently due to a deadlock - <braunr> youpi: it makes me think of the problem you sometimes have (and - had often with the page cache patch) - <braunr> in cthreads, mutex and condition operations are macros, and they - check the mutex/condition queue without holding the internal - mutex/condition lock - <braunr> i'm not sure where this can lead to, but it doesn't seem right - <pinotree> isn't that a bit dangerous? - <braunr> i believe it is - <braunr> i mean - <braunr> it looks dangerous - <braunr> but it may be perfectly safe - <pinotree> could it be? - <braunr> aiui, it's an optimization, e.g. "dont take the internal lock if - there are no thread to wake" - <braunr> but if there is a thread enqueuing itself at the same time, it - might not be waken - <pinotree> yeah - <braunr> pthreads don't have this issue - <braunr> and what i see looks like a deadlock - <pinotree> anything can happen between the unlocked checking and the - following instruction - <braunr> so i'm not sure how a situation working around a faulty - implementation would result in a deadlock with a correct one - <braunr> on the other hand, the error youpi reported - (http://lists.gnu.org/archive/html/bug-hurd/2012-07/msg00051.html) seems - to indicate something is deeply wrong with libports - <pinotree> it could also be the current code does not really "works around" - that, but simply implicitly relies on the so-generated behaviour - <braunr> luckily not often - <braunr> maybe - <braunr> i think we have to find and fix these issues before moving to - pthreads entirely - <braunr> (ofc, using pthreads to trigger those bugs is a good procedure) - <pinotree> indeed - <braunr> i wonder if tweaking the error checking mode of pthreads to abort - on EDEADLK is a good approach to detecting this problem - <braunr> let's try ! - <braunr> youpi: eh, i think i've spotted the libports ref mistake - <youpi> ooo! - <youpi> .oOo.!! - <gnu_srs> Same problem but different patches - <braunr> look at libports/bucket-iterate.c - <braunr> in the HURD_IHASH_ITERATE loop, pi->refcnt is incremented without - a lock - <youpi> Mmm, the incrementation itself would probably be compiled into an - INC, which is safe in UP - <youpi> it's an add currently actually - <youpi> 0x00004343 <+163>: addl $0x1,0x4(%edi) - <braunr> 40c4: 83 47 04 01 addl $0x1,0x4(%edi) - <youpi> that makes it SMP unsafe, but not UP unsafe - <braunr> right - <braunr> too bad - <youpi> that still deserves fixing :) - <braunr> the good side is my mind is already wired for smp - <youpi> well, it's actually not UP either - <youpi> in general - <youpi> when the processor is not able to do the add in one instruction - <braunr> sure - <braunr> youpi: looks like i'm wrong, refcnt is protected by the global - libports lock - <youpi> braunr: but aren't there pieces of code which manipulate the refcnt - while taking another lock than the global libports lock - <youpi> it'd not be scalable to use the global libports lock to protect - refcnt - <braunr> youpi: imo, the scalability issues are present because global - locks are taken all the time, indeed - <youpi> urgl - <braunr> yes .. - <braunr> when enabling mutex checks in libpthread, pfinet dies :/ - <braunr> grmbl, when trying to start "ls" using my deadlock-detection - libpthread, the terminal gets unresponsive, and i can't even use ps .. :( - <pinotree> braunr: one could say your deadlock detection works too - good... :P - <braunr> pinotree: no, i made a mistake :p - <braunr> it works now :) - <braunr> well, works is a bit fast - <braunr> i can't attach gdb now :( - <braunr> *sigh* - <braunr> i guess i'd better revert to a cthreads hurd and debug from there - <braunr> eh, with my deadlock-detection changes, recursive mutexes are now - failing on _pthread_self(), which for some obscure reason generates this - <braunr> => 0x0107223b <+283>: jmp 0x107223b - <__pthread_mutex_timedlock_internal+283> - <braunr> *sigh* - - -## IRC, freenode, #hurd, 2012-08-17 - - <braunr> aw, the thread storm i see isn't a deadlock - <braunr> seems to be mere contention .... - <braunr> youpi: what do you think of the way - ports_manage_port_operations_multithread determines it needs to spawn a - new thread ? - <braunr> it grabs a lock protecting the number of threads to determine if - it needs a new thread - <braunr> then releases it, to retake it right after if a new thread must be - created - <braunr> aiui, it could lead to a situation where many threads could - determine they need to create threads - <youpi> braunr: there's no reason to release the spinlock before re-taking - it - <youpi> that can indeed lead to too much thread creations - <braunr> youpi: a harder question - <braunr> youpi: what if thread creation fails ? :/ - <braunr> if i'm right, hurd servers simply never expect thread creation to - fail - <youpi> indeed - <braunr> and as some patterns have threads blocking until another produce - an event - <braunr> i'm not sure there is any point handling the failure at all :/ - <youpi> well, at least produce some output - <braunr> i added a perror - <youpi> so we know that happened - <braunr> async messaging is quite evil actually - <braunr> the bug i sometimes have with pfinet is usually triggered by - fakeroot - <braunr> it seems to use select a lot - <braunr> and select often destroys ports when it has something to return to - the caller - <braunr> which creates dead name notifications - <braunr> and if done often enough, a lot of them - <youpi> uh - <braunr> and as pfinet is creating threads to service new messages, already - existing threads are starved and can't continue - <braunr> which leads to pfinet exhausting its address space with thread - stacks (at about 30k threads) - <braunr> i initially thought it was a deadlock, but my modified libpthread - didn't detect one, and indeed, after i killed fakeroot (the whole - dpkg-buildpackage process hierarchy), pfinet just "cooled down" - <braunr> with almost all 30k threads simply waiting for requests to - service, and the few expected select calls blocking (a few ssh sessions, - exim probably, possibly others) - <braunr> i wonder why this doesn't happen with cthreads - <youpi> there's a 4k guard between stacks, otherwise I don't see anything - obvious - <braunr> i'll test my pthreads package with the fixed - ports_manage_port_operations_multithread - <braunr> but even if this "fix" should reduce thread creation, it doesn't - prevent the starvation i observed - <braunr> evil concurrency :p - - <braunr> youpi: hm i've just spotted an important difference actually - <braunr> youpi: glibc sched_yield is __swtch(), cthreads is - thread_switch(MACH_PORT_NULL, SWITCH_OPTION_DEPRESS, 10) - <braunr> i'll change the glibc implementation, see how it affects the whole - system - - <braunr> youpi: do you think bootsting the priority or cancellation - requests is an acceptable workaround ? - <braunr> boosting - <braunr> of* - <youpi> workaround for what? - <braunr> youpi: the starvation i described earlier - <youpi> well, I guess I'm not into the thing enough to understand - <youpi> you meant the dead port notifications, right? - <braunr> yes - <braunr> they are the cancellation triggers - <youpi> cancelling whaT? - <braunr> a blocking select for example - <braunr> ports_do_mach_notify_dead_name -> ports_dead_name -> - ports_interrupt_notified_rpcs -> hurd_thread_cancel - <braunr> so it's important they are processed quickly, to allow blocking - threads to unblock, reply, and be recycled - <youpi> you mean the threads in pfinet? - <braunr> the issue applies to all servers, but yes - <youpi> k - <youpi> well, it can not not be useful :) - <braunr> whatever the choice, it seems to be there will be a security issue - (a denial of service of some kind) - <youpi> well, it's not only in that case - <youpi> you can always queue a lot of requests to a server - <braunr> sure, i'm just focusing on this particular problem - <braunr> hm - <braunr> max POLICY_TIMESHARE or min POLICY_FIXEDPRI ? - <braunr> i'd say POLICY_TIMESHARE just in case - <braunr> (and i'm not sure mach handles fixed priority threads first - actually :/) - <braunr> hm my current hack which consists of calling swtch_pri(0) from a - freshly created thread seems to do the job eh - <braunr> (it may be what cthreads unintentionally does by acquiring a spin - lock from the entry function) - <braunr> not a single issue any more with this hack - <bddebian> Nice - <braunr> bddebian: well it's a hack :p - <braunr> and the problem is that, in order to boost a thread's priority, - one would need to implement that in libpthread - <bddebian> there isn't thread priority in libpthread? - <braunr> it's not implemented - <bddebian> Interesting - <braunr> if you want to do it, be my guest :p - <braunr> mach should provide the basic stuff for a partial implementation - <braunr> but for now, i'll fall back on the hack, because that's what - cthreads "does", and it's "reliable enough" - - <antrik> braunr: I don't think the locking approach in - ports_manage_port_operations_multithread() could cause issues. the worst - that can happen is that some other thread becomes idle between the check - and creating a new thread -- and I can't think of a situation where this - could have any impact... - <braunr> antrik: hm ? - <braunr> the worst case is that many threads will evalute spawn to 1 and - create threads, whereas only one of them should have - <antrik> braunr: I'm not sure perror() is a good way to handle the - situation where thread creation failed. this would usually happen because - of resource shortage, right? in that case, it should work in non-debug - builds too - <braunr> perror isn't specific to debug builds - <braunr> i'm building glibc packages with a pthreads-enabled hurd :> - <braunr> (which at one point run the test allocating and filling 2 GiB of - memory, which passed) - <braunr> (with a kernel using a 3/1 split of course, swap usage reached - something like 1.6 GiB) - <antrik> braunr: BTW, I think the observation that thread storms tend to - happen on destroying stuff more than on creating stuff has been made - before... - <braunr> ok - <antrik> braunr: you are right about perror() of course. brain fart -- was - thinking about assert_perror() - <antrik> (which is misused in some places in existing Hurd code...) - <antrik> braunr: I still don't see the issue with the "spawn" - locking... the only situation where this code can be executed - concurrently is when multiple threads are idle and handling incoming - request -- but in that case spawning does *not* happen anyways... - <antrik> unless you are talking about something else than what I'm thinking - of... - <braunr> well imagine you have idle threads, yes - <braunr> let's say a lot like a thousand - <braunr> and the server gets a thousand requests - <braunr> a one more :p - <braunr> normally only one thread should be created to handle it - <braunr> but here, the worst case is that all threads run internal_demuxer - roughly at the same time - <braunr> and they all determine they need to spawn a thread - <braunr> leading to another thousand - <braunr> (that's extreme and very unlikely in practice of course) - <antrik> oh, I see... you mean all the idle threads decide that no spawning - is necessary; but before they proceed, finally one comes in and decides - that it needs to spawn; and when the other ones are scheduled again they - all spawn unnecessarily? - <braunr> no, spawn is a local variable - <braunr> it's rather, all idle threads become busy, and right before - servicing their request, they all decide they must spawn a thread - <antrik> I don't think that's how it works. changing the status to busy (by - decrementing the idle counter) and checking that there are no idle - threads is atomic, isn't it? - <braunr> no - <antrik> oh - <antrik> I guess I should actually look at that code (again) before - commenting ;-) - <braunr> let me check - <braunr> no sorry you're right - <braunr> so right, you can't lead to that situation - <braunr> i don't even understand how i can't see that :/ - <braunr> let's say it's the heat :p - <braunr> 22:08 < braunr> so right, you can't lead to that situation - <braunr> it can't lead to that situation - - -## IRC, freenode, #hurd, 2012-08-18 - - <braunr> one more attempt at fixing netdde, hope i get it right this time - <braunr> some parts assume a ddekit thread is a cthread, because they share - the same address - <braunr> it's not as easy when using pthread_self :/ - <braunr> good, i got netdde work with pthreads - <braunr> youpi: for reference, there are now glibc, hurd and netdde - packages on my repository - <braunr> youpi: the debian specific patches can be found at my git - repository (http://git.sceen.net/rbraun/debian_hurd.git/ and - http://git.sceen.net/rbraun/debian_netdde.git/) - <braunr> except a freeze during boot (between exec and init) which happens - rarely, and the starvation which still exists to some extent (fakeroot - can cause many threads to be created in pfinet and pflocal), the - glibc/hurd packages have been working fine for a few days now - <braunr> the threading issue in pfinet/pflocal is directly related to - select, which the io_select_timeout patches should fix once merged - <braunr> well, considerably reduce at least - <braunr> and maybe fix completely, i'm not sure - - -## IRC, freenode, #hurd, 2012-08-27 - - <pinotree> braunr: wrt a78a95d in your pthread branch of hurd.git, - shouldn't that job theorically been done using pthread api (of course - after implementing it)? - <braunr> pinotree: sure, it could be done through pthreads - <braunr> pinotree: i simply restricted myself to moving the hurd to - pthreads, not augment libpthread - <braunr> (you need to remember that i work on hurd with pthreads because it - became a dependency of my work on fixing select :p) - <braunr> and even if it wasn't the reason, it is best to do these tasks - (replace cthreads and implement pthread scheduling api) separately - <pinotree> braunr: hm ok - <pinotree> implementing the pthread priority bits could be done - independently though - - <braunr> youpi: there are more than 9000 threads for /hurd/streamio kmsg on - ironforge oO - <youpi> kmsg ?! - <youpi> it's only /dev/klog right? - <braunr> not sure but it seems so - <pinotree> which syslog daemon is running? - <youpi> inetutils - <youpi> I've restarted the klog translator, to see whether when it grows - again - - <braunr> 6 hours and 21 minutes to build glibc on darnassus - <braunr> pfinet still runs only 24 threads - <braunr> the ext2 instance used for the build runs 2k threads, but that's - because of the pageouts - <braunr> so indeed, the priority patch helps a lot - <braunr> (pfinet used to have several hundreds, sometimes more than a - thousand threads after a glibc build, and potentially increasing with - each use of fakeroot) - <braunr> exec weights 164M eww, we definitely have to fix that leak - <braunr> the leaks are probably due to wrong mmap/munmap usage - -[[exec_memory_leaks]]. - - -### IRC, freenode, #hurd, 2012-08-29 - - <braunr> youpi: btw, after my glibc build, there were as little as between - 20 and 30 threads for pflocal and pfinet - <braunr> with the priority patch - <braunr> ext2fs still had around 2k because of pageouts, but that's - expected - <youpi> ok - <braunr> overall the results seem very good and allow the switch to - pthreads - <youpi> yep, so it seems - <braunr> youpi: i think my first integration branch will include only a few - changes, such as this priority tuning, and the replacement of - condition_implies - <youpi> sure - <braunr> so we can push the move to pthreads after all its small - dependencies - <youpi> yep, that's the most readable way - - -## IRC, freenode, #hurd, 2012-09-03 - - <gnu_srs> braunr: Compiling yodl-3.00.0-7: - <gnu_srs> pthreads: real 13m42.460s, user 0m0.000s, sys 0m0.030s - <gnu_srs> cthreads: real 9m 6.950s, user 0m0.000s, sys 0m0.020s - <braunr> thanks - <braunr> i'm not exactly certain about what causes the problem though - <braunr> it could be due to libpthread using doubly-linked lists, but i - don't think the overhead would be so heavier because of that alone - <braunr> there is so much contention sometimes that it could - <braunr> the hurd would have been better off with single threaded servers - :/ - <braunr> we should probably replace spin locks with mutexes everywhere - <braunr> on the other hand, i don't have any more starvation problem with - the current code - - -### IRC, freenode, #hurd, 2012-09-06 - - <gnu_srs> braunr: Yes you are right, the new pthread-based Hurd is _much_ - slower. - <gnu_srs> One annoying example is when compiling, the standard output is - written in bursts with _long_ periods of no output in between:-( - <braunr> that's more probably because of the priority boost, not the - overhead - <braunr> that's one of the big issues with our mach-based model - <braunr> we either give high priorities to our servers, or we can suffer - from message floods - <braunr> that's in fact more a hurd problem than a mach one - <gnu_srs> braunr: any immediate ideas how to speed up responsiveness the - pthread-hurd. It is annoyingly slow (slow-witted) - <braunr> gnu_srs: i already answered that - <braunr> it doesn't look that slower on my machines though - <gnu_srs> you said you had some ideas, not which. except for mcsims work. - <braunr> i have ideas about what makes it slower - <braunr> it doesn't mean i have solutions for that - <braunr> if i had, don't you think i'd have applied them ? :) - <gnu_srs> ok, how to make it more responsive on the console? and printing - stdout more regularly, now several pages are stored and then flushed. - <braunr> give more details please - <gnu_srs> it behaves like a loaded linux desktop, with little memory - left... - <braunr> details about what you're doing - <gnu_srs> apt-get source any big package and: fakeroot debian/rules binary - 2>&1 | tee ../binary.logg - <braunr> isee - <braunr> well no, we can't improve responsiveness - <braunr> without reintroducing the starvation problem - <braunr> they are linked - <braunr> and what you're doing involes a few buffers, so the laggy feel is - expected - <braunr> if we can fix that simply, we'll do so after it is merged upstream - - -### IRC, freenode, #hurd, 2012-09-07 - - <braunr> gnu_srs: i really don't feel the sluggishness you described with - hurd+pthreads on my machines - <braunr> gnu_srs: what's your hardware ? - <braunr> and your VM configuration ? - <gnu_srs> Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz - <gnu_srs> kvm -m 1024 -net nic,model=rtl8139 -net - user,hostfwd=tcp::5562-:22 -drive - cache=writeback,index=0,media=disk,file=hurd-experimental.img -vnc :6 - -cdrom isos/netinst_2012-07-15.iso -no-kvm-irqchip - <braunr> what is the file system type where your disk image is stored ? - <gnu_srs> ext3 - <braunr> and how much physical memory on the host ? - <braunr> (paste meminfo somewhere please) - <gnu_srs> 4G, and it's on the limit, 2 kvm instances+gnome,etc - <gnu_srs> 80% in use by programs, 14% in cache. - <braunr> ok, that's probably the reason then - <braunr> the writeback option doesn't help a lot if you don't have much - cache - <gnu_srs> well the other instance is cthreads based, and not so sluggish. - <braunr> we know hurd+pthreads is slower - <braunr> i just wondered why i didn't feel it that much - <gnu_srs> try to fire up more kvm instances, and do a heavy compile... - <braunr> i don't do that :) - <braunr> that's why i never had the problem - <braunr> most of the time i have like 2-3 GiB of cache - <braunr> and of course more on shattrath - <braunr> (the host of the sceen.net hurdboxes, which has 16 GiB of ram) - - -### IRC, freenode, #hurd, 2012-09-11 - - <gnu_srs> Monitoring the cthreads and the pthreads load under Linux shows: - <gnu_srs> cthread version: load can jump very high, less cpu usage than - pthread version - <gnu_srs> pthread version: less memory usage, background cpu usage higher - than for cthread version - <braunr> that's the expected behaviour - <braunr> gnu_srs: are you using the lifothreads gnumach kernel ? - <gnu_srs> for experimental, yes. - <gnu_srs> i.e. pthreads - <braunr> i mean, you're measuring on it right now, right ? - <gnu_srs> yes, one instance running cthreads, and one pthreads (with lifo - gnumach) - <braunr> ok - <gnu_srs> no swap used in either instance, will try a heavy compile later - on. - <braunr> what for ? - <gnu_srs> E.g. for memory when linking. I have swap available, but no swap - is used currently. - <braunr> yes but, what do you intend to measure ? - <gnu_srs> don't know, just to see if swap is used at all. it seems to be - used not very much. - <braunr> depends - <braunr> be warned that using the swap means there is pageout, which is one - of the triggers for global system freeze :p - <braunr> anonymous memory pageout - <gnu_srs> for linux swap is used constructively, why not on hurd? - <braunr> because of hard to squash bugs - <gnu_srs> aha, so it is bugs hindering swap usage:-/ - <braunr> yup :/ - <gnu_srs> Let's find them thenO:-), piece of cake - <braunr> remember my page cache branch in gnumach ? :) - -[[gnumach_page_cache_policy]]. - - <gnu_srs> not much - <braunr> i started it before fixing non blocking select - <braunr> anyway, as a side effect, it should solve this stability issue - too, but it'll probably take time - <gnu_srs> is that branch integrated? I only remember slab and the lifo - stuff. - <gnu_srs> and mcsims work - <braunr> no it's not - <braunr> it's unfinished - <gnu_srs> k! - <braunr> it correctly extends the page cache to all available physical - memory, but since the hurd doesn't scale well, it slows the system down - - -## IRC, freenode, #hurd, 2012-09-14 - - <braunr> arg - <braunr> darnassus seems to eat 100% cpu and make top freeze after some - time - <braunr> seems like there is an important leak in the pthreads version - <braunr> could be the lifothreads patch :/ - <cjbirk> there's a memory leak? - <cjbirk> in pthreads? - <braunr> i don't think so, and it's not a memory leak - <braunr> it's a port leak - <braunr> probably in the kernel - - -### IRC, freenode, #hurd, 2012-09-17 - - <braunr> nice, the port leak is actually caused by the exim4 loop bug - - -### IRC, freenode, #hurd, 2012-09-23 - - <braunr> the port leak i observed a few days ago is because of exim4 (the - infamous loop eating the cpu we've been seeing regularly) - -[[fork_deadlock]]? - - <youpi> oh - <braunr> next time it happens, and if i have the occasion, i'll examine the - problem - <braunr> tip: when you can't use top or ps -e, you can use ps -e -o - pid=,args= - <youpi> or -M ? - <braunr> haven't tested - - -### IRC, freenode, #hurd, 2013-01-26 - - <braunr> ah great, one of the recent fixes (probably select-eintr or - setitimer) fixed exim4 :) - - -## IRC, freenode, #hurd, 2012-09-23 - - <braunr> tschwinge: i committed the last hurd pthread change, - http://git.savannah.gnu.org/cgit/hurd/hurd.git/log/?h=master-pthreads - <braunr> tschwinge: please tell me if you consider it ok for merging - - -### IRC, freenode, #hurd, 2012-11-27 - - <youpi> braunr: btw, I forgot to forward here, with the glibc patch it does - boot fine, I'll push all that and build some almost-official packages for - people to try out what will come when eglibc gets the change in unstable - <braunr> youpi: great :) - <youpi> thanks for managing the final bits of this - <youpi> (and thanks for everybody involved) - <braunr> sorry again for the non obvious parts - <braunr> if you need the debian specific parts refined (e.g. nice commits - for procfs & others), i can do that - <youpi> I'll do that, no pb - <braunr> ok - <braunr> after that (well, during also), we should focus more on bug - hunting - - -## IRC, freenode, #hurd, 2012-10-26 - - <mcsim1> hello. What does following error message means? "unable to adjust - libports thread priority: Operation not permitted" It appears when I set - translators. - <mcsim1> Seems has some attitude to libpthread. Also following appeared - when I tried to remove translator: "pthread_create: Resource temporarily - unavailable" - <mcsim1> Oh, first message appears very often, when I use translator I set. - <braunr> mcsim1: it's related to a recent patch i sent - <braunr> mcsim1: hurd servers attempt to increase their priority on startup - (when a thread is created actually) - <braunr> to reduce message floods and thread storms (such sweet names :)) - <braunr> but if you start them as an unprivileged user, it fails, which is - ok, it's just a warning - <braunr> the second way is weird - <braunr> it normally happens when you're out of available virtual space, - not when shutting a translator donw - <mcsim1> braunr: you mean this patch: libports: reduce thread starvation on - message floods? - <braunr> yes - <braunr> remember you're running on darnassus - <braunr> with a heavily modified hurd/glibc - <braunr> you can go back to the cthreads version if you wish - <mcsim1> it's better to check translators privileges, before attempting to - increase their priority, I think. - <braunr> no - <mcsim1> it's just a bit annoying - <braunr> privileges can be changed during execution - <braunr> well remove it - <mcsim1> But warning should not appear. - <braunr> what could be done is to limit the warning to one occurrence - <braunr> mcsim1: i prefer that it appears - <mcsim1> ok - <braunr> it's always better to be explicit and verbose - <braunr> well not always, but very often - <braunr> one of the reasons the hurd is so difficult to debug is the lack - of a "message server" à la dmesg - -[[translator_stdout_stderr]]. - - -### IRC, freenode, #hurd, 2012-12-10 - - <youpi> braunr: unable to adjust libports thread priority: (ipc/send) - invalid destination port - <youpi> I'll see what package brought that - <youpi> (that was on a buildd) - <braunr> wow - <youpi> mkvtoolnix_5.9.0-1: - <pinotree> shouldn't that code be done in pthreads and then using such - pthread api? :p - <braunr> pinotree: you've already asked that question :p - <pinotree> i know :p - <braunr> the semantics of pthreads are larger than what we need, so that - will be done "later" - <braunr> but this error shouldn't happen - <braunr> it looks more like a random mach bug - <braunr> youpi: anything else on the console ? - <youpi> nope - <braunr> i'll add traces to know which step causes the error - - -#### IRC, freenode, #hurd, 2012-12-11 - - <youpi> braunr: mktoolnix seems like a reproducer for the libports thread - priority issue - <youpi> (3 times) - <braunr> youpi: thanks - <braunr> youpi: where is that tool packaged ? - <pinotree> he probably means the mkvtoolnix source - <braunr> seems so - <braunr> i don't find anything else - <youpi> that's it, yes - - -#### IRC, freenode, #hurd, 2013-03-01 - - <youpi> braunr: btw, "unable to adjust libports thread priority: (ipc/send) - invalid destination port" is actually not a sign of fatality - <youpi> bach recovered from it - <braunr> youpi: well, it never was a sign of fatality - <braunr> but it means that, for some reason, a process looses a right for a - very obscure reason :/ - <braunr> weird sentence, agreed :p - - -#### IRC, freenode, #hurd, 2013-06-14 - - <gnu_srs> Hi, when running check for gccgo the following occurs (multiple - times) locking up the console - <gnu_srs> unable to adjust libports thread priority: (ipc/send) invalid - destination port - <gnu_srs> (not locking up the console, it was just completely filled with - messages)) - <braunr> gnu_srs: are you running your translator as root ? - <braunr> or, do you have a translator running as an unprivileged user ? - <braunr> hm, invalid dest port - <braunr> that's a bug :p - <braunr> but i don't know why - <braunr> i'll have to take some time to track it down - <braunr> it might be a user ref overflow or something similarly tricky - <braunr> gnu_srs: does it happen everytime you run gccgo checks or only - after the system has been alive for some time ? - <braunr> (some time being at least a few hours, more probably days) - - -#### IRC, freenode, #hurd, 2013-07-05 - - <braunr> ok, found the bug about invalid ports when adjusting priorities - <braunr> thhe hurd must be plagued with wrong deallocations :( - <braunr> i have so many problems when trying to cleanly destroy threads - -[[libpthread/t/fix_have_kernel_resources]]. - - -#### IRC, freenode, #hurd, 2013-11-25 - - <braunr> youpi: btw, my last commit on the hurd repo fixes the urefs - overflow we've sometimes seen in the past in the priority adjusting code - of libports - - -#### IRC, freenode, #hurd, 2013-11-29 - -See also [[open_issues/libpthread/t/fix_have_kernel_resources]]. - - <braunr> there still are some leak ports making servers spawn threads with - non-elevated priorities :/ - <braunr> leaks* - <teythoon> issues with your thread destruction work ? - <teythoon> err, wait - <teythoon> why does a port leak cause that ? - <braunr> because it causes urefs overflows - <braunr> and the priority adjustment code does check errors :p - <teythoon> ^^ - <teythoon> ah yes, urefs... - <braunr> apparently it only affects the root file system - <teythoon> hm - <braunr> i'll spend an hour looking for it, and whatever i find, i'll - install the upstream debian packages so you can build glibc without too - much trouble - <teythoon> we need a clean build chroot on darnassus for this situation - <braunr> ah yes - <braunr> i should have time to set things up this week end - <braunr> 1: send (refs: 65534) - <braunr> i wonder what the first right is in the root file system - <teythoon> hm - <braunr> search doesn't help so i'm pretty sure it's a kernel object - <braunr> perhaps the host priv port - <teythoon> could be the thread port or something ? - <braunr> no, not the thread port - <teythoon> why would it have so many refs ? - <braunr> the task port maybe but it's fine if it overflows - <teythoon> also, some urefs are clamped at max, so maybe this is fine ? - <braunr> it may be fine yes - <braunr> err = get_privileged_ports (&host_priv, NULL); - <braunr> iirc, this function should pass copies of the name, not increment - the urefs counter - <braunr> it may behave differently if built statically - <teythoon> o_O y would it ? - <braunr> no idea - <braunr> something doesn't behave as it should :) - <braunr> i'm not asking why, i'm asking where :) - <braunr> the proc server is also affected - <braunr> so it does look like it has something to do with bootstrap - <teythoon> I'm not surprised :/ - - -#### IRC, freenode, #hurd, 2013-11-30 - - <braunr> so yes, the host_priv port gets a reference when calling - get_privileged_ports - <braunr> but only in the rootfs and proc servers, probably because others - use the code path to fetch it from proc - <teythoon> ah - <teythoon> well, it shouldn't behave differently - <braunr> ? - <teythoon> get_privileged_ports - <braunr> get_privileged_ports is explictely described to cache references - <teythoon> i don't get it - <teythoon> you said it behaved differently for proc and the rootfs - <teythoon> that's undesireable, isn't it ? - <braunr> yes - <teythoon> ok - <braunr> so it should behave differently than it does - <teythoon> yes - <teythoon> right - <braunr> teythoon: during your work this summer, have you come across the - bootstrap port of a task ? - <braunr> i wonder what the bootstrap port of the root file system is - <braunr> maybe i got the description wrong since references on host or - master are deallocated where get_privileged_ports is used .. - <teythoon> no, I do not believe i did anything bootstrap port related - <braunr> ok - <braunr> i don't need that any more fortunately - <braunr> i just wonder how someone could write a description so error-prone - .. - <braunr> and apparently, this problem should affect all servers, but for - some reason i didn't see it - <braunr> there, problem fixed - <teythoon> ? - <braunr> last leak eliminated - <teythoon> cool :) - <teythoon> how ? - <braunr> i simply deallocate host_priv in addition to the others when - adjusting thread priority - <braunr> as simple as that .. - <teythoon> uh - <teythoon> sure ? - <braunr> so many system calls just for reference counting - <braunr> yes - <teythoon> i did that, and broke the rootfs - <braunr> well i'm using one right now - <teythoon> ok - <braunr> maybe i should let it run a bit :) - <teythoon> no, for me it failed on the first write - <braunr> teythoon: looks weird - <teythoon> so i figured it was wrong to deallocate that port - <braunr> i'll reboot it and see if there may be a race - <teythoon> thought i didn't get a reference after all or something - <teythoon> I believe there is a race in ext2fs - <braunr> teythoon: that's not good news for me - <teythoon> when doing fsysopts --update / (which remounts /) - <teythoon> sometimes, the system hangs - <braunr> :/ - <teythoon> might be a deadlock, or the rootfs dies and noone notices - <teythoon> with my protected payload stuff, the system would reboot instead - of just hanging - <braunr> oh - <teythoon> which might point to a segfault in ext2fs - <teythoon> maybe the exception message carries a bad payload - <braunr> makes sense - <braunr> exception handling in ext2fs is messy .. - <teythoon> braunr: and, doing sleep 0.1 before remounting / makes the - problem less likely to appear - <braunr> ugh - <teythoon> and system load on my host system seems to affect this - <teythoon> but it is hard to tell - <teythoon> sometimes, this doesn't show up at all - <teythoon> sometimes several times in a row - <braunr> the system load might simply indicate very short lived processes - <braunr> (or threads) - <teythoon> system load on my host - <braunr> ah - <teythoon> this makes me believe that it is a race somewhere - <teythoon> all of this - <braunr> well, i can't get anything wrong with my patched rootfs - <teythoon> braunr: ok, maybe I messed up - <braunr> or maybe you were very unlucky - <braunr> and there is a rare race - <braunr> but i'll commit anyway - <teythoon> no, i never got it to work, always hung at the first write - <braunr> it won't be the first or last rare problem we'll have to live with - <braunr> hm - <braunr> then you probably did something wrong, yes - <braunr> that's reassuring - - -### IRC, freenode, #hurd, 2013-03-11 - - <braunr> youpi: oh btw, i noticed a problem with the priority adjustement - code - <braunr> a thread created by a privileged server (e.g. an ext2fs - translator) can then spawn a server from a node owned by an unprivileged - user - <braunr> which inherits the priority - <braunr> easy to fix but worth saying to keep in mind - <youpi> uh - <youpi> indeed - -### IRC, freenode, #hurd, 2013-07-01 - - <youpi> braunr: it seems as if pfinet is not prioritized enough - <youpi> I'm getting network connectivity issues when the system is quite - loaded - <braunr> loaded with what ? - <braunr> it could be ext2fs having a lot more threads than other servers - <youpi> building packages - <youpi> I'm talking about the buildds - <braunr> ok - <braunr> ironforge or others ? - <youpi> they're having troubles uploading packages while building stuff - <youpi> ironforge and others - <youpi> that happened already in the past sometimes - <youpi> but at the moment it's really pronounced - <braunr> i don't think it's a priority issue - <braunr> i think it's swapping - <youpi> ah, that's not impossible indeed - <youpi> but why would it swap? - <youpi> there's a lot of available memory - <braunr> a big file is enough - <braunr> it pushes anonymous memory out - <youpi> to fill 900MiB memory ? - <braunr> i see 535M of swap on if - <braunr> yes - <youpi> ironforge is just building libc - <braunr> and for some reason, swapping is orders of magnitude slower than - anything else - <youpi> not linking it yet - <braunr> i also see 1G of free memory on it - <youpi> that's what I meant with 900MiB - <braunr> so at some point, it needed a lot of memory, caused swapping - <braunr> and from time to time it's probably swapping back - <youpi> well, pfinet had all the time to swap back already - <youpi> I don't see why it should be still suffering from it - <braunr> swapping is a kernel activity - <youpi> ok, but once you're back, you're back - <youpi> unless something else pushes you out - <braunr> if the kernel is busy waiting for the default pager, nothing makes - progress - <braunr> (eccept the default pager hopefully) - <youpi> sure but pfinet should be back already, since it does work - <youpi> so I don't see why it should wait for something - <braunr> the kernel is waiting - <braunr> and the kernel isn't preemptibl - <braunr> e - <braunr> although i'm not sure preemption is the problem here - <youpi> well - <youpi> what I don't understand is what we have changed that could have so - much impact - <youpi> the only culprit I can see is the priorities we have changed - recently - <braunr> do you mean it happens a lot more frequently than before ? - <youpi> yes - <youpi> way - <braunr> ok - <youpi> ironforge is almost unusable while building glibc - <youpi> I've never seen that - <braunr> that's weird, i don't have these problems on darnassus - <braunr> but i think i reboot it more often - <braunr> could be a scalability issue then - <braunr> combined with the increased priorities - <braunr> if is indeed running full time on the host, whereas swapping - issues show the cpu being almost idle - <braunr> loadavg is high too so i guess there are many threads - <braunr> 0 971 3 -20 -20 1553 305358625 866485906 523M 63M * S<o - ? 13hrs /hurd/ext2fs.static -A /dev/hd0s2 - <braunr> 0 972 3 -20 -20 1434 125237556 719443981 483M 5.85M * S<o - ? 13hrs /hurd/ext2fs.static -A /dev/hd0s3 - <braunr> around 1k5 each - <youpi> that's quite usual - <braunr> could be the priorities then - <braunr> but i'm afraid that if we lower them, the number of threads will - grow out of control - <braunr> (good thing is i'm currently working on a way to make libpthread - actually remove kernel resources) - <youpi> but the priorities should be the same in ext2fs and pfinet, - shouldn't they? - <braunr> yes but ext2 has a lot more threads than pfinet - <braunr> the scheduler only sees threads, we don't have a grouping feature - <youpi> right - <braunr> we also should remove priority depressing in glibc - <braunr> (in sched_yield) - <braunr> it affects spin locks - - <braunr> youpi: is it normal to see priorities of 26 ? - <youpi> braunr: we have changed the nice factor - <braunr> ah, factor - <youpi> Mm, I'm however realizing the gnumach kernel running these systems - hasn't been upgraded in a while - <youpi> it may not even have the needed priority levels - <braunr> ar euare you using top right now on if ? - <braunr> hm no i don't see it any more - <braunr> well yes, could be the priorities .. - <youpi> I've rebooted with an upgraded kernel - <youpi> no issue so far - <youpi> package uploads will tell me on the long run - <braunr> i bet it's also a scalability issue - <youpi> but why would it appear now only? - <braunr> until the cache and other data containers start to get filled, - processing is fast enough that we don't see it hapenning - <youpi> sure, but I haven't seen that in the past - <braunr> oh it's combined with the increased priorities - <youpi> even after a week building packages - <braunr> what i mean is, increased priorities don't affect much if threads - porcess things fast - <braunr> things get longer with more data, and then increased prioritis - give more time to these threads - <braunr> and that's when the problem appears - <youpi> but increased priorities give more time to the pfinet threads too, - don't they? - <braunr> yes - <youpi> so what is different ? - <braunr> but again, there are a lot more threads elsewhere - <braunr> with a lot more data to process - <youpi> sure, but that has alwasy been so - <braunr> hm - <youpi> really, 1k5 threads does not surprise me at all :) - <youpi> 10k would - <braunr> there aren't all active either - <youpi> yes - <braunr> but right, i don't know why pfinet would be given less time than - other threads .. - <braunr> compared to before - <youpi> particularly on xen-based buildds - <braunr> libpthread is slower than cthreads - <youpi> where it doesn't even have to wait for netdde - <braunr> threads need more quanta to achieve the same ting - <braunr> perhaps processing could usually be completed in one go before, - and not any more - <braunr> we had a discussion about this with antrik - - <braunr> youpi: concerning the buildd issue, i don't think pfinet is - affected actually - <braunr> but the applications using the network may be - <youpi> why using the network would be a difference ? - <braunr> normal applications have a lower priority - <braunr> what i mean is, pfinet simply has nothing to do, because normal - applications don't have enough cpu time - <braunr> (what you said earlier seemed to imply pfinet had issues, i don't - think it has) - <braunr> it should be easy to test by pinging the machine while under load - <braunr> we should also check the priority of the special thread used to - handle packets, both in pfinet and netdde - <braunr> this one isn't spawned by libports and is likely to have a lower - priority as well - - <braunr> youpi: you're right, something very recent slowed things down a - lot - <braunr> perhaps the new priority factor - <braunr> well not the factor but i suppose the priority range has been - increased - -[[nice_vs_mach_thread_priorities]]. - - <youpi> braunr: haven't had any upload issue so far - <youpi> over 20 uploads - <youpi> while it was usually 1 every 2 before... - <youpi> so it was very probably the kernel missing the priorities levels - <braunr> ok - <braunr> i think i've had the same problem on another virtual machine - <braunr> with a custom kernel i built a few weeks ago - <braunr> same kind of issue i guess - <braunr> it's fine now, and always was on darnassus - - -## IRC, freenode, #hurd, 2012-12-05 - - <braunr> tschwinge: i'm currently working on a few easy bugs and i have - planned improvements for libpthreads soon - <pinotree> wotwot, which ones? - <braunr> pinotree: first, fixing pthread_cond_timedwait (and everything - timedsomething actually) - <braunr> pinotree: then, fixing cancellation - <braunr> pinotree: and last but not least, optimizing thread wakeup - <braunr> i also want to try replacing spin locks and see if it does what i - expect - <pinotree> which fixes do you plan applying to cond_timedwait? - <braunr> see sysdeps/generic/pt-cond-timedwait.c - <braunr> the FIXME comment - <pinotree> ah that - <braunr> well that's important :) - <braunr> did you have something else in mind ? - <pinotree> hm, __pthread_timedblock... do you plan fixing directly there? i - remember having seem something related to that (but not on conditions), - but wasn't able to see further - <braunr> it has the same issue - <braunr> i don't remember the details, but i wrote a cthreads version that - does it right - <braunr> in the io_select_timeout branch - <braunr> see - http://git.savannah.gnu.org/cgit/hurd/hurd.git/tree/libthreads/cancel-cond.c?h=rbraun/select_timeout - for example - * pinotree looks - <braunr> what matters is the msg_delivered member used to synchronize - sleeper and waker - <braunr> the waker code is in - http://git.savannah.gnu.org/cgit/hurd/hurd.git/tree/libthreads/cprocs.c?h=rbraun/select_timeout - <pinotree> never seen cthreads' code before :) - <braunr> soon you shouldn't have any more reason to :p - <pinotree> ah, so basically the cthread version of the pthread cleanup - stack + cancelation (ie the cancel hook) broadcasts the condition - <braunr> yes - <pinotree> so a similar fix would be needed in all the places using - __pthread_timedblock, that is conditions and mutexes - <braunr> and that's what's missing in glibc that prevents deploying a - pthreads based hurd currently - <braunr> no that's unrelated - <pinotree> ok - <braunr> the problem is how __pthread_block/__pthread_timedblock is - synchronized with __pthread_wakeup - <braunr> libpthreads does exactly the same thing as cthreads for that, - i.e. use messages - <braunr> but the message alone isn't enough, since, as explained in the - FIXME comment, it can arrive too late - <braunr> it's not a problem for __pthread_block because this function can - only resume after receiving a message - <braunr> but it's a problem for __pthread_timedblock which can resume - because of a timeout - <braunr> my solution is to add a flag that says whether a message was - actually sent, and lock around sending the message, so that the thread - resume can accurately tell in which state it is - <braunr> and drain the message queue if needed - <pinotree> i see, race between the "i stop blocking because of timeout" and - "i stop because i got a message" with the actual check for the real cause - <braunr> locking around mach_msg may seem overkill but it's not in - practice, since there can only be one message at most in the message - queue - <braunr> and i checked that in practice by limiting the message queue size - and check for such errors - <braunr> but again, it would be far better with mutexes only, and no spin - locks - <braunr> i wondered for a long time why the load average was so high on the - hurd under even "light" loads - <braunr> now i know :) - - -## IRC, freenode, #hurd, 2012-12-27 - - <youpi> btw, good news: the installer works with libpthread - <youpi> (well, at least boots, I haven't tested the installation) - <braunr> i can do that if the image is available publically - <braunr> youpi: the one thing i suspect won't work right is the hurd - console :/ - <braunr> so we might need to not enable it by default - <youpi> braunr: you mean the mode setting? - <braunr> youpi: i don't know what's wrong with the hurd console, but it - seems to deadlock with pthreads - <youpi> ah? - <youpi> I don't have such issue - <braunr> ah ? i need to retest that then - -Same issue as [[term_blocking]] perhaps? - - -## IRC, freenode, #hurd, 2013-01-06 - - <youpi> it seems fakeroot has become slow as hell - -[[pfinet_timers]]. - - <braunr> fakeroot is the main source of dead name notifications - <braunr> well, a very heavy one - <braunr> with pthreads hurd servers, their priority is raised, precisely to - give them time to handle those dead name notifications - <braunr> which slows everything else down, but strongly reduces the rate at - which additional threads are created to handle dn notifications - <braunr> so this is expected - <youpi> ok :/ - <braunr> which is why i mentioned a rewrite of io_select into a completely - synchronous io_poll - <braunr> so that the client themselves remove their requests, instead of - the servers doing it asynchronously when notified - <youpi> by "slows everything else down", you mean, if the servers do take - cpu time? - <braunr> but considering the amount of messaging it requires, it will be - slow on moderate to large fd sets with frequent calls (non blocking or - low timeout) - <braunr> yes - <youpi> well here the problem is not really it gets slowed down - <youpi> but that e.g. for gtk+2.0 build, it took 5h cpu time - <youpi> (and counting) - <braunr> ah, the hurd with pthreads is noticeably slower too - <braunr> i'm not sure why, but i suspect the amount of internal function - calls could account for some of the overhead - <youpi> I mean the fakeroot process - <youpi> not the server process - <braunr> hum - <braunr> that's not normal :) - <youpi> that's what I meant - <braunr> well, i should try to build gtk+20 some day - <braunr> i've been building glibc today and it's going fine for now - <youpi> it's the install stage which poses problem - <youpi> I've noticed it with the hurd package too - <braunr> the hurd is easier to build - <braunr> that's a good test case - <braunr> there are many times when fakeroot just doesn't use cpu, and it - doesn't look like a select timeout issue (it still behaved that way with - my fixed branch) - <youpi> in general, pfinet is taking really a lot of cpu time - <youpi> that's surprising - <braunr> why ? - <braunr> fakeroot uses it a lot - <youpi> I know - <youpi> but still - <youpi> 40% cpu time is not normal - <youpi> I don't see why it would need so much cpu time - <braunr> 17:57 < braunr> but considering the amount of messaging it - requires, it will be slow on moderate to large fd sets with frequent - calls (non blocking or low timeout) - <youpi> by "it", what did you mean? - <youpi> I thought you meant the synchronous select implementation - <braunr> something irrelevant here - <braunr> yes - <braunr> what matters here is the second part of my sentence, which is what - i think happens now - <youpi> you mean it's the IPC overhead which is taking so much time? - <braunr> i mean, it doesn't matter if io_select synchronously removes - requests, or does it by destroying ports and relying on notifications, - there are lots of messages in this case anyway - <braunr> yes - <youpi> why "a lot" ? - <youpi> more than one per select call? - <braunr> yes - <youpi> why ? - <braunr> one per fd - <braunr> then one to wait - <youpi> there are two in faked - <braunr> hum :) - <braunr> i remember the timeout is low - <braunr> but i don't remember its value - <youpi> the timeout is NULL in faked - <braunr> the client then - <youpi> the client doesn't use select - <braunr> i must be confused - <braunr> i thought it did through the fakeroot library - <braunr> but yes, i see the same behaviour, 30 times more cpu for pfinet - than faked-tcp - <braunr> or let's say between 10 to 30 - <braunr> and during my tests, these were the moments the kernel would - create lots of threads in servers and fail because of lack of memory, - either kernel memory, or virtual in the client space (filled with thread - stacks) - <braunr> it could be due to threads spinning too much - <braunr> (inside pfinet) - <youpi> attaching a gdb shows it mostly inside __pthread_block - <youpi> uh, how awful pfinet's select is - <youpi> a big global lock - <youpi> whenever something happens all threads get woken up - <pinotree> BKL! - * pinotree runs - <braunr> we have many big hurd locks :p - <youpi> it's rather a big translator lock - <braunr> more than a global lock it seems, a global condvar too, isn't it ? - <youpi> sure - <braunr> we have a similar problem with the hurd-specific cancellation - code, it's in my todo list with io_select - <youpi> ah, no, the condvar is not global - - -## IRC, freenode, #hurd, 2013-01-14 - - <braunr> *sigh* thread cancellable is totally broken :( - <braunr> cancellation* - <braunr> it looks like playing with thread cancellability can make some - functions completely restart - <braunr> (e.g. one call to printf to write twice its output) - -[[git_duplicated_content]], [[git-core-2]]. - - * braunr is cooking a patch to fix pthread cancellation in - pthread_cond_{,timed}wait, smells good - <braunr> youpi: ever heard of something that would make libc functions - "restart" ? - <youpi> you mean as a feature, or as a bug ? - <braunr> when changing the pthread cancellation state of a thread, i - sometimes see printf print its output twice - <youpi> or perhaps after a signal dispatch? - <braunr> i'll post my test code - <youpi> that could be a duplicate write - <youpi> due to restarting after signal - <braunr> http://www.sceen.net/~rbraun/pthreads_test_cancel.c - #include <stdio.h> - #include <stdarg.h> - #include <stdlib.h> - #include <pthread.h> - #include <unistd.h> - - static pthread_cond_t cond = PTHREAD_COND_INITIALIZER; - static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; - static int predicate; - static int ready; - static int cancelled; - - static void - uncancellable_printf(const char *format, ...) - { - int oldstate; - va_list ap; - - va_start(ap, format); - pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate); - vprintf(format, ap); - pthread_setcancelstate(oldstate, &oldstate); - va_end(ap); - } - - static void * - run(void *arg) - { - uncancellable_printf("thread: setting ready\n"); - ready = 1; - uncancellable_printf("thread: spin until cancellation is sent\n"); - - while (!cancelled) - sched_yield(); - - uncancellable_printf("thread: locking mutex\n"); - pthread_mutex_lock(&mutex); - uncancellable_printf("thread: waiting for predicate\n"); - - while (!predicate) - pthread_cond_wait(&cond, &mutex); - - uncancellable_printf("thread: unlocking mutex\n"); - pthread_mutex_unlock(&mutex); - uncancellable_printf("thread: exit\n"); - return NULL; - } - - int - main(int argc, char *argv[]) - { - pthread_t thread; - - uncancellable_printf("main: create thread\n"); - pthread_create(&thread, NULL, run, NULL); - uncancellable_printf("main: spin until thread is ready\n"); - - while (!ready) - sched_yield(); - - uncancellable_printf("main: sending cancellation\n"); - pthread_cancel(thread); - uncancellable_printf("main: setting cancelled\n"); - cancelled = 1; - uncancellable_printf("main: joining thread\n"); - pthread_join(thread, NULL); - uncancellable_printf("main: exit\n"); - return EXIT_SUCCESS; - } - <braunr> youpi: i'd see two calls to write, the second because of a signal, - as normal, as long as the second call resumes, but not restarts after - finishing :/ - <braunr> or restarts because nothing was done (or everything was entirely - rolled back) - <youpi> well, with an RPC you may not be sure whether it's finished or not - <braunr> ah - <youpi> we don't really have rollback - <braunr> i don't really see the difference with a syscall there - <youpi> the kernel controls the interruption in the case of the syscall - <braunr> except that write is normally atomic if i'm right - <youpi> it can't happen on the way back to userland - <braunr> but that could be exactly the same with RPCs - <youpi> while perhaps it can happen on the mach_msg back to userland - <braunr> back to userland ok, back to the application, no - <braunr> anyway, that's a side issue - <braunr> i'm fixing a few bugs in libpthread - <braunr> and noticed that - <braunr> (i should soon have patches to fix - at least partially - thread - cancellation and timed blocking) - <braunr> i was just wondering how cancellation how handled in glibc wrt - libpthread - <youpi> I don't know - <braunr> (because the non standard hurd cancellation has nothing to do with - pthread cancellation)à - <braunr> ok - <braunr> s/how h/is h/ - - -### IRC, freenode, #hurd, 2013-01-15 - - <tschwinge> braunr: Re »one call to printf to write twice its output«: - sounds familiar: - http://www.gnu.org/software/hurd/open_issues/git_duplicated_content.html - and http://www.gnu.org/software/hurd/open_issues/git-core-2.html - <braunr> tschwinge: what i find strange with the duplicated operations i've - seen is that i merely use pthreads and printf, nothing else - <braunr> no setitimer, no alarm, no select - <braunr> so i wonder how cancellation/syscall restart is actually handled - in our glibc - <braunr> but i agree with you on the analysis - - -### IRC, freenode, #hurd, 2013-01-16 - - <braunr> neal: do you (by any chance) remember if there could possibly be - spurious wakeups in your libpthread implementation ? - <neal> braunr: There probably are. - <neal> but I don't recall - - <braunr> i think the duplicated content issue is due to the libmach/glibc - mach_msg wrapper - <braunr> which restarts a message send if interrupted - <tschwinge> Hrm, depending on which point it has been interrupted you mean? - <braunr> yes - <braunr> not sure yet and i could be wrong - <braunr> but i suspect that if interrupted after send and during receive, - the restart might be wrongfully done - <braunr> i'm currently reworking the timed* pthreads functions, doing the - same kind of changes i did last summer when working on select (since - implement the timeout at the server side requires pthread_cond_timedwait) - <braunr> and i limit the message queue size of the port used to wake up - threads to 1 - <braunr> and it seems i have the same kind of problems, i.e. blocking - because of a second, unexpected send - <braunr> i'll try using __mach_msg_trap directly and see how it goes - <tschwinge> Hrm, mach/msg.c:__mach_msg does look correct to me, but yeah, - won't hurd to confirm this by looking what direct usage of - __mach_msg_trap is doing. - <braunr> tschwinge: can i ask if you still have a cthreads based hurd - around ? - <braunr> tschwinge: and if so, to send me libthreads.so.0.3 ... :) - <tschwinge> braunr: darnassus:~tschwinge/libthreads.so.0.3 - <braunr> call 19c0 <mach_msg@plt> - <braunr> so, cthreads were also using the glibc wrapper - <braunr> and i never had a single MACH_SEND_INTERRUPTED - <braunr> or a busy queue :/ - <braunr> (IOW, no duplicated messages, and the wrapper indeed looks - correct, so it's something else) - <tschwinge> (Assuming Mach is doing the correct thing re interruptions, of - course...) - <braunr> mach doesn't implement it - <braunr> it's explicitely meant to be done in userspace - <braunr> mach merely reports the error - <braunr> i checked the osfmach code of libmach, it's almost exactly the - same as ours - <tschwinge> Yeah, I meant Mach returns the interurption code but anyway - completed the RPC. - <braunr> ok - <braunr> i don't expect mach wouldn't do it right - <braunr> the only difference in osf libmach is that, when retrying, - MACH_SEND_INTERRUPT|MACH_RCV_INTERRUPT are both masked (for both the - send/send+receive and receive cases) - <tschwinge> Hrm. - <braunr> but they say it's for performance, i.e. mach won't take the slow - path because of unexpected bits in the options - <braunr> we probably should do the same anyway - - -### IRC, freenode, #hurd, 2013-01-17 - - <braunr> tschwinge: i think our duplicated RPCs come from - hurd/intr-msg.c:148 (err == MACH_SEND_INTERRUPTED but !(option & - MACH_SEND_MSG)) - <braunr> a thread is interrupted by a signal meant for a different thread - <braunr> hum no, still not that .. - <braunr> or maybe .. :) - <tschwinge> Hrm. Why would it matter for for the current thread for which - reason (different thread) mach_msg_trap returns *_INTERRUPTED? - <braunr> mach_msg wouldn't return it, as explained in the comment - <braunr> the signal thread would, to indicate the send was completed but - the receive must be retried - <braunr> however, when retrying, the original user_options are used again, - which contain MACH_SEND_MSG - <braunr> i'll test with a modified version that masks it - <braunr> tschwinge: hm no, doesn't fix anything :( - - -### IRC, freenode, #hurd, 2013-01-18 - - <braunr> the duplicated rpc calls is one i find very very frustrating :/ - <youpi> you mean the dup writes we've seen lately? - <braunr> yes - <youpi> k - - -### IRC, freenode, #hurd, 2013-01-19 - - <braunr> all right, i think the duplicated message sends are due to thread - creation - <braunr> the duplicated message seems to be sent by the newly created - thread - <braunr> arg no, misread - - -### IRC, freenode, #hurd, 2013-01-20 - - <braunr> tschwinge: youpi: about the diplucated messages issue, it seems to - be caused by two threads (with pthreads) doing an rpc concurrently - <braunr> duplicated* - - -### IRC, freenode, #hurd, 2013-01-21 - - <braunr> ah, found something interesting - <braunr> tschwinge: there seems to be a race on our file descriptors - <braunr> the content written by one thread seems to be retained somewhere - and another thread writing data to the file descriptor will resend what - the first already did - <braunr> it could be a FILE race instead of fd one though - <braunr> yes, it's not at the fd level, it's above - <braunr> so good news, seems like the low level message/signalling code - isn't faulty here - <braunr> all right, simple explanation: our IO_lockfile functions are - no-ops - <pinotree> braunr: i found that out days ago, and samuel said they were - okay - -[[glibc]], `flockfile`/`ftrylockfile`/`funlockfile`. - - -## IRC, freenode, #hurd, 2013-01-15 - - <braunr> hmm, looks like subhurds have been broken by the pthreads patch :/ - <braunr> arg, we really do have broken subhurds :(( - <braunr> time for an immersion in the early hurd bootstrapping stuff - <tschwinge> Hrm. Narrowed down to cthreads -> pthread you say. - <braunr> i think so - <braunr> but i think the problem is only exposed - <braunr> it was already present before - <braunr> even for the main hurd, i sometimes have systems blocking on exec - <braunr> there must be a race there that showed far less frequently with - cthreads - <braunr> youpi: we broke subhurds :/ - <youpi> ? - <braunr> i can't start one - <braunr> exec seems to die and prevent the root file system from - progressing - <braunr> there must be a race, exposed by the switch to pthreads - <braunr> arg, looks like exec doesn't even reach main :( - <braunr> now, i'm wondering if it could be the tls support that stops exec - <braunr> although i wonder why exec would start correctly on a main hurd, - and not on a subhurd :( - <braunr> i even wonder how much progress ld.so.1 is able to make, and don't - have much idea on how to debug that - - -### IRC, freenode, #hurd, 2013-01-22 - - <braunr> hm, subhurds seem to be broken because of select - <braunr> damn select ! - <braunr> hm i see, we can't boot a subhurd that still uses libthreads from - a main hurd that doesn't - <braunr> the linker can't find it and doesn't start exec - <braunr> pinotree: do you understand what the fmh function does in - sysdeps/mach/hurd/dl-sysdep.c ? - <braunr> i think we broke subhurds by fixing vm_map with size 0 - <pinotree> braunr: no idea, but i remember thomas talking about this code - -[[vm_map_kernel_bug]] - - <braunr> it checks for KERN_INVALID_ADDRESS and KERN_NO_SPACE - <braunr> and calls assert_perror(err); to make sure it's one of them - <braunr> but now, KERN_INVALID_ARGUMENT can be returned - <braunr> ok i understand what it does - <braunr> and youpi has changed the code, so he does too - <braunr> (now i'm wondering why he didn't think of it when we fixed vm_map - size with 0 but his head must already be filled with other things so ..) - <braunr> anyway, once this is dealt with, we get subhurds back :) - <braunr> yes, with a slight change, my subhurd starts again \o/ - <braunr> youpi: i found the bug that prevents subhurds from booting - <braunr> it's caused by our fixing of vm_map with size 0 - <braunr> when ld.so.1 starts exec, the code in - sysdeps/mach/hurd/dl-sysdep.c fails because it doesn't expect the new - error code we introduced - <braunr> (the fmh functions) - <youpi> ah :) - <youpi> good :) - <braunr> adding KERN_INVALID_ARGUMENT to the list should do the job, but if - i understand the code correctly, checking if fmhs isn't 0 before calling - vm_map should do the work too - <braunr> s/do the work/work/ - <braunr> i'm not sure which is the preferred way - <youpi> otherwise I believe fmh could be just fixed to avoid calling vm_map - in the !fmhs case - <braunr> yes that's what i currently do - <braunr> at the start of the loop, just after computing it - <braunr> seems to work so far - - -## IRC, freenode, #hurd, 2013-01-22 - - <braunr> i have almost completed fixing both cancellation and timeout - handling, but there are still a few bugs remaining - <braunr> fyi, the related discussion was - https://lists.gnu.org/archive/html/bug-hurd/2012-08/msg00057.html - - -## IRC, freenode, #hurd, 2014-01-01 - - <youpi> braunr: I have an issue with tls_thread_leak - <youpi> int main(void) { - <youpi> pthread_create(&t, NULL, foo, NULL); - <youpi> pthread_exit(0); - <youpi> } - <youpi> this fails at least with the libpthread without your libpthread - thread termination patch - <youpi> because for the main thread, tcb->self doesn't contain thread_self - <youpi> where is tcb->self supposed to be initialized for the main thread? - <youpi> there's also the case of fork()ing from main(), then calling - pthread_exit() - <youpi> (calling pthread_exit() from the child) - <youpi> the child would inherit the tcb->self value from the parent, and - thus pthread_exit() would try to kill the father - <youpi> can't we still do tcb->self = self, even if we don't keep a - reference over the name? - <youpi> (the pthread_exit() issue above should be fixed by your thread - termination patch actually) - <youpi> Mmm, it seems the thread_t port that the child inherits actually - properly references the thread of the child, and not the thread of the - father? - <youpi> “For the name we use for our own thread port, we will insert the - thread port for the child main user thread after we create it.” Oh, good - :) - <youpi> and, “Skip the name we use for any of our own thread ports.”, good - too :) - <braunr> youpi: reading - <braunr> youpi: if we do tcb->self = self, we have to keep the reference - <braunr> this is strange though, i had tests that did exactlt what you're - talking about, and they didn't fail - <youpi> why? - <braunr> if you don't keep the reference, it means you deallocate self - <youpi> with the thread termination patch, tcb->self is not used for - destruction - <braunr> hum - <braunr> no it isn't - <braunr> but it must be deallocated at some point if it's not temporary - <braunr> normally, libpthread should set it for the main thread too, i - don't understand - <youpi> I don't see which code is supposed to do it - <youpi> sure it needs to be deallocated at some point - <youpi> but does tcb->self has to wear the reference? - <braunr> init_routine should do it - <braunr> it calls __pthread_create_internal - <braunr> which allocates the tcb - <braunr> i think at some point, __pthread_setup should be called for it too - <youpi> but what makes pthread->kernel_thread contain the port for the - thread? - <braunr> but i have to check that - <braunr> __pthread_thread_alloc does that - <braunr> so normally it should work - <braunr> is your libpthread up to date as well ? - <youpi> no, as I said it doesn't contain the thread destruction patch - <braunr> ah - <braunr> that may explain - <youpi> but the tcb->self uninitialized issue happens on darnassus too - <youpi> it just doesn't happen to crash because it's not used - <braunr> that's weird :/ - <youpi> see ~youpi/test.c there for instance - <braunr> humpf - <braunr> i don't see why :/ - <braunr> i'll debug that later - <braunr> youpi: did you find the problem ? - <youpi> no - <youpi> I'm working on fixing the libpthread hell in the glibc debian - package :) - <youpi> i.e. replace a dozen patches with a git snapshot - <braunr> ah you reverted commit - <braunr> +a - <braunr> i imagine it's hairy :) - <youpi> not too much actually - <braunr> wow :) - <youpi> with the latest commits, things have converged - <youpi> it's now about small build details - <youpi> I just take time to make sure I'm getting the same source code in - the end :) - <braunr> :) - <braunr> i hope i can determine what's going wrong tonight - <braunr> youpi: avec mach_print, je vois bien self setté par la libpthread - .. - <youpi> mais à autre chose que 0 ? - <braunr> oui - <braunr> bizarrement, l'autre thread n'as pas la même valeur - <braunr> tu es bien sûr que c'est self que tu affiches avec l'assembleur ? - <braunr> oops, english - <youpi> see test2 - <youpi> so I'm positive - <braunr> well, there obviously is a bug - <braunr> but are you certain your assembly code displays the thread port - name ? - <youpi> I'm certain it displays tcb->self - <braunr> oh wait, hexadecimal, ok - <youpi> and the value happens to be what mach_thread_self returns - <braunr> ah right - <youpi> ah, right, names are usually decimals :) - <braunr> hm - <braunr> what's the problem with test2 ? - <youpi> none - <braunr> ok - <youpi> I was just checking what happens on fork from another thread - <braunr> ok i do have 0x68 now - <braunr> so the self field gets erased somehow - <braunr> 15:34 < youpi> this fails at least with the libpthread without - your libpthread thread termination patch - <braunr> how does it fail ? - <youpi> ../libpthread/sysdeps/mach/pt-thread-halt.c:44: - __pthread_thread_halt: Unexpected error: (ipc/send) invalid destination - port. - <braunr> hm - <braunr> i don't have that problem on darnassus - <youpi> with the new libc? - <braunr> the pthread destruction patch actually doesn't use the tcb->self - name if i'm right - <braunr> yes - <braunr> what is tcb->self used for ? - <youpi> it used to be used by pt-thread-halt - <youpi> but is darnassus using your thread destruction patch? - <youpi> as I said, since your thread destruction pathc doesn't use - tcb->self, it doesn't have the issue - <braunr> the patched libpthread merely uses the sysdeps kernel_thread - member - <braunr> ok - <youpi> it's the old libpthread against the new libc which has issues - <braunr> yes it is - <braunr> so for me, the only thing to do is make sure tcb->self remains - valid - <braunr> we could simply add a third user ref but i don't like the idea - <youpi> well, as you said the issue is rather that tcb->self gets - overwritten - <youpi> there is no reason why it should - <braunr> the value is still valid when init_routine exits, so it must be in - libc - <youpi> or perhaps for some reason tls gets initialized twice - <braunr> maybe - <youpi> and thus what libpthread's init writes to is not what's used later - <braunr> i've add a print in pthread_create, to see if self actually got - overwritten - <braunr> and it doesn't - <braunr> there is a disrepancy between the tcb member in libpthread and - what libc uses for tls - <braunr> added* - <braunr> (the print is at the very start of pthread_create, and displays - the thread name of the caller only) - <youpi> well, yes, for the main thread libpthread shouldn't be allocating a - new tcb - <youpi> and just use the existing one - <braunr> ? - <youpi> the main thread's tcb is initialized before the threading library - iirc - <braunr> hmm - <braunr> it would make sense if we actually had non-threaded programs :) - <youpi> at any rate, the address of the tcb allocated by libpthread is not - put into registers - <braunr> how does it get there for the other threads ? - <youpi> __pthread_setup does it - <braunr> so - <braunr> looks like dl_main is called after init_routine - <braunr> and it then calls init_tls - <braunr> init_tls returns the tcb for the main thread, and that's what - overrides the libpthread one - <youpi> yes, _hurd_tls_init is called very early, before init_routine - <youpi> __pthread_create_internal could fetch the tcb pointer from gs:0 - when it's the main thread - <braunr> so there is something i didn't get right - <braunr> i thought _hurd_tls_init was called as part of dl_main - <youpi> well, it's not a bug of yours, it has always been bug :) - <braunr> which is called *after* init_routine - <braunr> and that explains why the libpthread tcb isn't the one installed - in the thread register - <braunr> i can actually check that quite easily - <youpi> where do you see dl_main called after init_routine? - <braunr> well no i got that wrong somehow - <braunr> or i'm unable to find it again - <braunr> let's see - <braunr> init_routine is called by init which is called by _dl_init_first - <braunr> which i can only find in the macro RTLD_START_SPECIAL_INIT - <braunr> with print traces, i see dl_main called before init_routine - <braunr> so yes, libpthread should reuse it - <braunr> the tcb isn't overriden, it's just never installed - <braunr> i'm not sure how to achieve that cleanly - <youpi> well, it is installed, by _hurd_tls_init - <youpi> it's the linker which creates the main thread's tcb - <youpi> and calls _hurd_tls_init to install it - <youpi> before the thread library enters into action - <braunr> agreed - - -### IRC, freenode, #hurd, 2014-01-14 - - <braunr> btw, are you planning to do something with regard to the main - thread tcb initialization issue ? - <youpi> well, I thought you were working on it - <braunr> ok - <braunr> i wasn't sure - - -### IRC, freenode, #hurd, 2014-01-19 - - <braunr> i have some fixup code for the main thread tcb - <braunr> but it sometimes crashes on tcb deallocation - <braunr> is there anything particular that you would know about the tcb of - the main thread ? - <braunr> (that could help explaining this) - <youpi> Mmmm, I don't think there is anything particular - <braunr> doesn't look like the first tcb can be reused safely - <braunr> i think we should instead update the thread register to point to - the pthread tcb - <youpi> what do you mean by "the first tcb" exactly? - - -## IRC, freenode, #hurd, 2014-01-03 - - <gg0> braunr: hurd from your repo can't boot. restored debian one - <braunr> gg0: it does boot - <braunr> gg0: but you need everything (gnumach and glibc) in order to make - it work - <braunr> i think youpi did take care of compatibility with older kernels - <teythoon> braunr: so do we need a rebuilt libc for the latest hurd from - git ? - <braunr> teythoon: no, the hurd isn't the problem - <teythoon> ok - <teythoon> good - <braunr> the problem is the libports_stability patch - <teythoon> what about it ? - <braunr> the hurd can't work correctly without it since the switch to - pthreads - <braunr> because of subtle bugs concerning resource recycling - <teythoon> ok - <braunr> these have been fixed recently by youpi and me (youpi fixed them - exactly as i did, which made my life very easy when merging :)) - <braunr> there is also the problem of the stack sizes, which means the hurd - servers could use 2M stacks with an older glibc - <braunr> or perhaps it chokes on an error when attempting to set the stack - size because it was unsupported - <braunr> i don't know - <braunr> that may be what gg0 suffered from - <gg0> yes, both gnumach and eglibc were from debian. seems i didn't - manually upgrade eglibc from yours - <gg0> i'll reinstall them now. let's screw it up once again - <braunr> :) - <braunr> bbl - <gg0> ok it boots - <gg0> # apt-get install - {hurd,hurd-dev,hurd-libs0.3}=1:0.5.git20131101-1+rbraun.7 - {libc0.3,libc0.3-dev,libc0.3-dbg,libc-dev-bin}=2.17-97+hurd.0+rbraun.1+threadterm.1 - <gg0> there must a simpler way - <gg0> besides apt-pinning - <gg0> making it a real "experimental" release might help with -t option for - instance - <gg0> btw locales still segfaults - <gg0> rpctrace from teythoon gets stuck at - http://paste.debian.net/plain/74072/ - <gg0> ("rpctrace locale-gen", last 300 lines) |