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diff --git a/open_issues/rpc_to_self_with_rendez-vous_leading_to_duplicate_port_destroy.mdwn b/open_issues/rpc_to_self_with_rendez-vous_leading_to_duplicate_port_destroy.mdwn deleted file mode 100644 index 9db92250..00000000 --- a/open_issues/rpc_to_self_with_rendez-vous_leading_to_duplicate_port_destroy.mdwn +++ /dev/null @@ -1,163 +0,0 @@ -[[!meta copyright="Copyright © 2011 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 -License|/fdl]]."]]"""]] - -[[!tag open_issue_hurd]] - -[RPC to self with rendez-vous leading to duplicate port -destroy](http://lists.gnu.org/archive/html/bug-hurd/2011-03/msg00045.html) - -IRC, freenode, #hurd, 2011-03-14 - - <antrik> youpi: I wonder, why does the root FS call diskfs_S_dir_lookup() - at all?... - <youpi> errr, because a client asked for it? - <youpi> (problem with RPCs is you can't easily know where they come from :) - ) - <youpi> (especially when it's the root fs...) - <antrik> ah, it's about a client request... didn't see that - <youpi> well, I just said "is called", yes - <antrik> I do not really understand though why it tries to reauthenticate - against itself... - <antrik> I fear my memory of the lookup mechanism grew a bit dim - <youpi> see the source - <youpi> it's about a translated entry - <antrik> (and I never fully understood some aspects anyways...) - <youpi> it needs to start the translated entry as another user, possibly - <antrik> yes, but a translated entry normally would be served by *another* - process?... - <youpi> sure, but ext2fs has to prepare it - <youpi> thus reauthenticate to prepare the correct set of rights - <antrik> prepare what? - <youpi> rights - <youpi> so the process is not root, doesn't have / opened as root, etc. - <antrik> rights for what? - <youpi> err, about everything - <antrik> IIRC the reauthentication is done by the parent FS on the port to - the *translated* node - <antrik> and the translated node should be a different process?... - <youpi> that's not what I read in the source - <youpi> fshelp_fetch_root - <youpi> ports[INIT_PORT_CRDIR] = reauth (getcrdir ()); - <youpi> here, getcrdir() returns ext2fs itself - <antrik> well, perhaps the issue is that I have no idea what - fshelp_fetch_root() does, nor why it is called here... - <youpi> it notably starts the translator that dir_lookup is looking at, if - needed - <youpi> possibly as a different user, thus reauthentication of CRDIR - <antrik> so this is about a port that is passed to the translator being - started? - <youpi> no - <youpi> well, depends on what you mean by "port" - <youpi> it's about reauthenticating a port to be passed to the translator - being started - <youpi> and for that a rendez-vous port is needed for the reauthentication - <youpi> and that's the one at stake - <antrik> yeah, I meant the port that is reauthenticated - <antrik> what is CRDIR? - <youpi> current root dir ... - <antrik> so the parent translator passes it's own root dir to the child - translator; and the issue is that for the root FS the root dir points to - the root FS itself... - <youpi> yes - <antrik> OK, that makes sense - <youpi> (but that's only one example, rgrep mach_port_destroy hurd/ show - other potential issues) - <antrik> well, that's actually what I wanted to mention next... why is the - rendez-vous port destroyed, instead of just deallocating the port right - and letting reference counting to it's thing?... - <antrik> do its thing - <youpi> "just to make sure" I guess - <antrik> it's pretty obvious that this will cause trouble for any RPC - referencing itself... - <youpi> well, follow-up with that on the list - <youpi> with roland/tb in CC - <youpi> only they would know any real reason for destroy - <youpi> btw, if you knew how we could make _hurd_select()'s raw __mach_msg - call be interruptible by signals, that'll permit to fix sudo - <youpi> (damn, I need sleep, my tenses are all wrong) - <antrik> BTW, does this cause any actual trouble?... - <antrik> I don't know much about interruption... cfhammer might have a - better idea, he look into that stuff quite a bit AIUI - <antrik> looked - <antrik> (hehe, it's not only your tenses... guess there's something in the - ether ;-) ) - <youpi> it makes sudo, mailq, etc. fail sometimes - <antrik> I mean the rendez-vous thing - <youpi> that's it, yes - <youpi> sudo etc. fail at least due to this - <antrik> so these are two different problems that both affect sudo? - <antrik> (rendez-vous and interruption I mean) - <youpi> yes - <youpi> with my patch the buildds have much fewer issues, but still some - <youpi> (my interrupt-related patch) - <youpi> I'm installing a s/destroy/deallocate/ version of ext2fs on the - buildds, we'll see how it behaves - <youpi> (it fixes my testcase at least) - <antrik> interrupt-related patch? - <antrik> only thing interrupt-related I remember was the reauthentication - race... - <youpi> that's what I mean - <antrik> well, cfhammer investigated this is quite some depth, explaining - quite well why the race is only mitigated but still exists... problem is - that we didn't know how to fix it properly - <antrik> because nobody seems to understand the cancellation code, except - perhaps for Roland and Thomas - <antrik> (and I'm not even entirely sure about them :-) ) - <antrik> I think his findings and our conclusions are documented on the - ML... - <youpi> by "much fewer issues", I mean that some of the symptoms have - disappeared, others haven't - <antrik> BTW, couldn't the rendez-vous thing be worked around by simply - ignoring the errors from the failing deallocate?... - <youpi> no, failing deallocate are actually dangerous - <antrik> why? - <youpi> since the name might have been reused for something else in the - meanwhile - <youpi> that's the whole point of the warning I had added in the kernel - itself - <antrik> I see - <youpi> such things really deserve tracking, since they can have any kind - of consequence - <antrik> does Mach try to reuse names quickly, rather than only after - wrapping around?... - <youpi> it seems to - <antrik> OK, then this is a serious problem indeed - <youpi> (note: I rarely divine issues when there aren't actual frequent - symptoms :) ) - <antrik> well, the problem with the warning is that it only shows in the - cases that do *not* cause a problem... so it's hard to associate them - with any specific issues - <youpi> well, most of the time the port is not reused quickly enough - <youpi> so in most case it shows up more often than causing problem - -IRC, freenode, #hurd, 2011-03-14 - - <youpi> ok, mach_port_deallocate actually can't be used - <youpi> since mach_reply_port() returns a receive right, not a send right - * youpi guesses he will really have to manage to understand all that port - stuff completely - <antrik> oh, right - <antrik> youpi: hm... now I'm confused though. if one client holds a - receive right, the other client (or in this case the same process) should - have a send or send-once right -- these should *not* share the same name - in my understanding - <antrik> destroying the receive right should turn the send right into a - dead name - <antrik> so unless I'm missing something, the destroy shouldn't be a - problem, and there must be something else going wrong - <antrik> hm... actually I'm probably wrong - <antrik> yeah, definitely wrong. receive rights and "ordinary" send rights - share the name. only send-once rights are special - <antrik> I wonder whether the problem could be worked around by using a - send-once right... - <antrik> mach_port_mod_refs(mach_task_self(), name, - MACH_PORT_RIGHT_RECEIVE, -1) can be used to deallocate only the receive - right - <antrik> oh, you already figured that out :-) |