path: root/open_issues/libpthread.mdwn
diff options
authorSamuel Thibault <>2015-02-18 00:58:35 +0100
committerSamuel Thibault <>2015-02-18 00:58:35 +0100
commit49a086299e047b18280457b654790ef4a2e5abfa (patch)
treec2b29e0734d560ce4f58c6945390650b5cac8a1b /open_issues/libpthread.mdwn
parente2b3602ea241cd0f6bc3db88bf055bee459028b6 (diff)
Revert "rename open_issues.mdwn to service_solahart_jakarta_selatan__082122541663.mdwn"
This reverts commit 95878586ec7611791f4001a4ee17abf943fae3c1.
Diffstat (limited to 'open_issues/libpthread.mdwn')
1 files changed, 2414 insertions, 0 deletions
diff --git a/open_issues/libpthread.mdwn b/open_issues/libpthread.mdwn
new file mode 100644
index 00000000..0294b008
--- /dev/null
+++ b/open_issues/libpthread.mdwn
@@ -0,0 +1,2414 @@
+[[!meta copyright="Copyright © 2010, 2011, 2012, 2013, 2014 Free Software
+Foundation, Inc."]]
+[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
+is included in the section entitled [[GNU Free Documentation
+[[!tag open_issue_glibc open_issue_libpthread]]
+# 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?
+ <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/ 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 :(
+ <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:
+ <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.
+ <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>
+ <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
+ ( 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
+ <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> 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 ( and
+ <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
+### 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 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 ? :)
+ <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)
+ <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,
+ <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
+### 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
+#### 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
+ <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
+ for example
+ * pinotree looks
+ <braunr> what matters is the msg_delivered member used to synchronize
+ sleeper and waker
+ <braunr> the waker code is in
+ <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
+ <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>
+ #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:
+ and
+ <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 ... :)
+ <tschwinge> braunr: darnassus:~tschwinge/
+ <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 &
+ <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 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
+ <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 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
+## 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
+ <gg0> ("rpctrace locale-gen", last 300 lines)