Messages in this thread | | | Date | Wed, 19 Oct 2011 13:01:24 -0700 | From | Greg KH <> | Subject | Re: Patch Upstream: cputimer: Cure lock inversion |
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On Wed, Oct 19, 2011 at 09:41:52PM +0200, Thomas Gleixner wrote: > On Wed, 19 Oct 2011, Greg KH wrote: > > > On Wed, Oct 19, 2011 at 11:39:14AM -0400, Gregs git-bot wrote: > > > commit: bcd5cff7216f9b2de0a148cc355eac199dc6f1cf > > > From: Peter Zijlstra <a.p.zijlstra@chello.nl> > > > Date: Mon, 17 Oct 2011 11:50:30 +0200 > > > Subject: cputimer: Cure lock inversion > > > > > > There's a lock inversion between the cputimer->lock and rq->lock; > > > notably the two callchains involved are: > > > > > > update_rlimit_cpu() > > > sighand->siglock > > > set_process_cpu_timer() > > > cpu_timer_sample_group() > > > thread_group_cputimer() > > > cputimer->lock > > > thread_group_cputime() > > > task_sched_runtime() > > > ->pi_lock > > > rq->lock > > > > > > scheduler_tick() > > > rq->lock > > > task_tick_fair() > > > update_curr() > > > account_group_exec() > > > cputimer->lock > > > > > > Where the first one is enabling a CLOCK_PROCESS_CPUTIME_ID timer, and > > > the second one is keeping up-to-date. > > > > > > This problem was introduced by e8abccb7193 ("posix-cpu-timers: Cure > > > SMP accounting oddities"). > > > > There is no such patch in Linus's tree that I can find. So, what > > problem is this really trying to cure here and what kernel did it show > > up in? > > Oops. It's in 3.0.7 > > commit 249cf808ba1a0d403fe7c476a74b66e2bc0a8e53 > Author: Peter Zijlstra <a.p.zijlstra@chello.nl> > Date: Thu Sep 1 12:42:04 2011 +0200 > > posix-cpu-timers: Cure SMP wobbles > > commit d670ec13178d0fd8680e6742a2bc6e04f28f87d8 upstream. > > and that patch introduced the above deadlock, which is cured by: > > commit bcd5cff7216f9b2de0a148cc355eac199dc6f1cf > Author: Peter Zijlstra <a.p.zijlstra@chello.nl> > Date: Mon Oct 17 11:50:30 2011 +0200 > > cputimer: Cure lock inversion
Thanks for the explanation. I should have it all straightened out now.
greg k-h
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