kernel/cputimer-cure-lock-inversion.patch
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Linux 3.1-rc10
Copy nouveau updates patch from F16
Fix deadlock in POSIX cputimer code (rhbz #746485)
2011-10-19 01:28:40 -04:00

74 lines
2.3 KiB
Diff

Subject: cputimer: Cure lock inversion
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Mon Oct 17 11:50:30 CEST 2011
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").
Cure the problem by removing the cputimer->lock and rq->lock nesting,
this leaves concurrent enablers doing duplicate work, but the time
wasted should be on the same order otherwise wasted spinning on the
lock and the greater-than assignment filter should ensure we preserve
monotonicity.
Reported-by: Dave Jones <davej@redhat.com>
Reported-by: Simon Kirby <sim@hostway.ca>
Cc: stable@kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/posix-cpu-timers.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
Index: linux-2.6/kernel/posix-cpu-timers.c
===================================================================
--- linux-2.6.orig/kernel/posix-cpu-timers.c
+++ linux-2.6/kernel/posix-cpu-timers.c
@@ -274,9 +274,7 @@ void thread_group_cputimer(struct task_s
struct task_cputime sum;
unsigned long flags;
- spin_lock_irqsave(&cputimer->lock, flags);
if (!cputimer->running) {
- cputimer->running = 1;
/*
* The POSIX timer interface allows for absolute time expiry
* values through the TIMER_ABSTIME flag, therefore we have
@@ -284,8 +282,11 @@ void thread_group_cputimer(struct task_s
* it.
*/
thread_group_cputime(tsk, &sum);
+ spin_lock_irqsave(&cputimer->lock, flags);
+ cputimer->running = 1;
update_gt_cputime(&cputimer->cputime, &sum);
- }
+ } else
+ spin_lock_irqsave(&cputimer->lock, flags);
*times = cputimer->cputime;
spin_unlock_irqrestore(&cputimer->lock, flags);
}