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Date: Sun, 14 Oct 2007 00:04:33 -0400 From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> To: Oleg Nesterov <oleg@...sign.ru> Cc: Andrew Morton <akpm@...ux-foundation.org>, viro@....linux.org.uk, kamezawa.hiroyu@...fujitsu.com, linux-kernel@...r.kernel.org, sam@...nborg.org, netdev@...r.kernel.org, Pavel Emelyanov <xemul@...nvz.org>, Sukadev Bhattiprolu <sukadev@...ibm.com>, Paul Menage <menage@...gle.com>, "Eric W. Biederman" <ebiederm@...ssion.com> Subject: Re: 2.6.23-mm1 thread exit_group issue * Oleg Nesterov (oleg@...sign.ru) wrote: > On 10/12, Andrew Morton wrote: > > > > On Fri, 12 Oct 2007 15:47:59 -0400 > > Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote: > > > > > Hi Andrew, > > > > > > I noticed a regression between 2.6.23-rc8-mm2 and 2.6.23-mm1 (with your > > > hotfixes). User space threads seems to receive a ERESTART_RESTARTBLOCK > > > as soon as a thread does a pthread_join on them. The previous behavior > > > was to wait for them to exit by taking a futex. > > No, the reason is that pthread_join() succeeds while it shouldn't. The main > thread does exit_group() and kills the sub-thread sleeping in nanosleep. > ERESTART_RESTARTBLOCK is not delivered to the user-space (sub-thread is dying), > it is just reported by gdb. > > > > I provide a toy program that shows the problem. On 2.6.23-rc8-mm2, it > > > loops forever (as it should). On 2.6.23-mm1, it exits after 10 seconds. > > I bet something like this > > void *threda(void *arg) > { > for (;;) > pause(); > return NULL; > } > > int main(void) > { > pthread_t tid; > > pthread_create(&tid, NULL, thread, NULL); > pthread_join(tid, NULL); > > return 0; > } > > won't work as well. > > > > Any idea on what may cause this problem ? > > Because do_fork() doesn't use parent_tidptr. At all! So it is very clear > why 2.6.23-mm1 is broken. > > > Bisection shows that this problem is caused by these two patches: > > > > pid-namespaces-allow-cloning-of-new-namespace.patch > > This? http://marc.info/?l=linux-mm-commits&m=118712242002039 > > Pavel, this patch has a subtle difference compared to what we discussed on > containers list. It moves put_user(parent_tidptr) from copy_process() to > do_fork(), so we don't report child's pid if copy_process() failed. I do > not think this is bad, but Eric seems to disagree with such a change. > > But I can't understand why Andrew sees the same problem _after_ this patch! > > And which patch removed the "put_user(nr, parent_tidptr)" chunk? > > Andrew, could I get the kernel source after bisection somehow? (I am not > familiar with guilt, will try to study it later) > > Mathieu, could you try the patch below? > Hi Oleg, Yes, it runs fine with this patch. Thanks, Mathieu > Oleg. > > --- kernel/fork.c~ 2007-10-13 15:41:35.000000000 +0400 > +++ kernel/fork.c 2007-10-13 15:41:41.000000000 +0400 > @@ -1443,6 +1443,9 @@ long do_fork(unsigned long clone_flags, > task_pid_nr_ns(p, current->nsproxy->pid_ns) : > task_pid_vnr(p); > > + if (clone_flags & CLONE_PARENT_SETTID) > + put_user(nr, parent_tidptr); > + > if (clone_flags & CLONE_VFORK) { > p->vfork_done = &vfork; > init_completion(&vfork); > -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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