[tip:sched/core] sched: Fix the racy usage of thread_group_cputimer() in fastpath_timer_check()
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From: tip-bot for Oleg Nesterov on 18 Jun 2010 06:30 Commit-ID: 8d1f431cbec115a780cd551ab1b4955c125f8d31 Gitweb: http://git.kernel.org/tip/8d1f431cbec115a780cd551ab1b4955c125f8d31 Author: Oleg Nesterov <oleg(a)redhat.com> AuthorDate: Fri, 11 Jun 2010 20:04:46 +0200 Committer: Ingo Molnar <mingo(a)elte.hu> CommitDate: Fri, 18 Jun 2010 10:46:57 +0200 sched: Fix the racy usage of thread_group_cputimer() in fastpath_timer_check() fastpath_timer_check()->thread_group_cputimer() is racy and unneeded. It is racy because another thread can clear ->running before thread_group_cputimer() takes cputimer->lock. In this case thread_group_cputimer() will set ->running = true again and call thread_group_cputime(). But since we do not hold tasklist or siglock, we can race with fork/exit and copy the wrong results into cputimer->cputime. It is unneeded because if ->running == true we can just use the numbers in cputimer->cputime we already have. Change fastpath_timer_check() to copy cputimer->cputime into the local variable under cputimer->lock. We do not re-check ->running under cputimer->lock, run_posix_cpu_timers() does this check later. Note: we can add more optimizations on top of this change. Signed-off-by: Oleg Nesterov <oleg(a)redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> LKML-Reference: <20100611180446.GA13025(a)redhat.com> Signed-off-by: Ingo Molnar <mingo(a)elte.hu> --- kernel/posix-cpu-timers.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-) diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index d5dbef5..f66bdd3 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -1287,7 +1287,10 @@ static inline int fastpath_timer_check(struct task_struct *tsk) if (sig->cputimer.running) { struct task_cputime group_sample; - thread_group_cputimer(tsk, &group_sample); + spin_lock(&sig->cputimer.lock); + group_sample = sig->cputimer.cputime; + spin_unlock(&sig->cputimer.lock); + if (task_cputime_expired(&group_sample, &sig->cputime_expires)) return 1; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |