Commit-ID: 8d1f431cbec115a780cd551ab1b4955c125f8d31
Gitweb: http://git.kernel.org/tip/8d1f431cbec115a780cd551ab1b4955c125f8d31
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Fri, 11 Jun 2010 20:04:46 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <20100611180446.GA13025@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
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;
}
--
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