diff options
authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-10-17 11:50:30 +0200
committerThomas Gleixner <tglx@linutronix.de>2011-10-18 11:36:59 +0200
commitbcd5cff7216f9b2de0a148cc355eac199dc6f1cf (patch)
parent899e3ee404961a90b828ad527573aaaac39f0ab1 (diff)
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"). 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> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: stable@kernel.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Link: http://lkml.kernel.org/r/1318928713.21167.4.camel@twins Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
1 files changed, 4 insertions, 3 deletions
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index c8008dd58ef2..640ded8f5c48 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -274,9 +274,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
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_struct *tsk, struct task_cputime *times)
* 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);