path: root/kernel/sched.c
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authorOleg Nesterov <oleg@redhat.com>2010-06-11 20:04:46 +0200
committerIngo Molnar <mingo@elte.hu>2010-06-18 10:46:57 +0200
commit8d1f431cbec115a780cd551ab1b4955c125f8d31 (patch)
treef71e707f0ff495582bd2f43017c87b2ac6ec519d /kernel/sched.c
parent0bdd2ed4138ec04e09b4f8165981efc99e439f55 (diff)
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@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20100611180446.GA13025@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
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