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[PATCH] ITIMER_REAL: fix possible deadlock and race

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As Steven Rostedt pointed out, there are 2 problems with ITIMER_REAL
timers.

1. do_setitimer() does not call del_timer_sync() in case
   when the timer is not pending (it_real_value() returns 0).
   This is wrong, the timer may still be running, and it can
   rearm itself.

2. It calls del_timer_sync() with tsk->sighand->siglock held.
   This is deadlockable, because timer's handler needs this
   lock too.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2005-06-28 20:44:47 -07:00 committed by Linus Torvalds
parent b36bbb6c3d
commit f01b1b0baa
1 changed files with 6 additions and 2 deletions
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8
kernel/itimer.c
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@ -153,11 +153,15 @@ int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
switch (which) { switch (which) {
case ITIMER_REAL: case ITIMER_REAL:
again:
spin_lock_irq(&tsk->sighand->siglock); spin_lock_irq(&tsk->sighand->siglock);
interval = tsk->signal->it_real_incr; interval = tsk->signal->it_real_incr;
val = it_real_value(tsk->signal); val = it_real_value(tsk->signal);
if (val) /* We are sharing ->siglock with it_real_fn() */
del_timer_sync(&tsk->signal->real_timer); if (try_to_del_timer_sync(&tsk->signal->real_timer) < 0) {
spin_unlock_irq(&tsk->sighand->siglock);
goto again;
}
tsk->signal->it_real_incr = tsk->signal->it_real_incr =
timeval_to_jiffies(&value->it_interval); timeval_to_jiffies(&value->it_interval);
it_real_arm(tsk, timeval_to_jiffies(&value->it_value)); it_real_arm(tsk, timeval_to_jiffies(&value->it_value));