Commit f01b1b0b authored Jun 28, 2005 by Oleg Nesterov Committed by Linus Torvalds Jun 28, 2005

[PATCH] ITIMER_REAL: fix possible deadlock and race



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>

parent b36bbb6c

kernel/itimer.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -153,11 +153,15 @@ int do_setitimer(int which, struct itimerval value, struct itimerval ovalue)

		switch (which) {
		case ITIMER_REAL:
		again:
		spin_lock_irq(&tsk->sighand->siglock);
		interval = tsk->signal->it_real_incr;
		val = it_real_value(tsk->signal);
		if (val)
		del_timer_sync(&tsk->signal->real_timer);
		/* We are sharing ->siglock with it_real_fn() */
		if (try_to_del_timer_sync(&tsk->signal->real_timer) < 0) {
		spin_unlock_irq(&tsk->sighand->siglock);
		goto again;
		}
		tsk->signal->it_real_incr =
		timeval_to_jiffies(&value->it_interval);
		it_real_arm(tsk, timeval_to_jiffies(&value->it_value));