[RFC][PATCH] Avoid race w/ posix-cpu-timer and exiting tasks

john stultz
2006-06-13T00:25:13Z

Hey Ingo,
We've occasionally come across OOPSes in posix-cpu-timer thread (as
well as tripping over the BUG_ON(tsk->exit_state there) where it appears
the task we're processing exits out on us while we're using it.

Thus this fix tries to avoid running the posix-cpu-timers on a task that
is exiting.

I'm not sure if it is the proper fix, so I wanted some extra eyes to
look it over. We're testing it to see if we can still trigger any of the
OOPSes (the BUG_ON is removed, so that won't catch us anymore), but if
you have any thoughts I'd be interested in them.

thanks
-john

--- 2.6-rt/kernel/posix-cpu-timers.c 2006-06-11 15:38:58.000000000 -0500
+++ devrt/kernel/posix-cpu-timers.c 2006-06-12 10:52:20.000000000 -0500
@@ -1290,12 +1290,15 @@

#undef UNEXPIRED

- BUG_ON(tsk->exit_state);
-
/*
* Double-check with locks held.
*/
read_lock(&tasklist_lock);
+ /* Make sure the task doesn't exit under us. */
+ if(unlikely(tsk->exit_state)) {
+ read_unlock(&tasklist_lock);
+ return;
+ }
spin_lock(&tsk->sighand->siglock);

/*