[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>
diff --git a/kernel/itimer.c b/kernel/itimer.c
index 1dc988e..a72cb0e 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -153,11 +153,15 @@
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));