]> pilppa.com Git - linux-2.6-omap-h63xx.git/commit
posix-timers: fix deletion race
authorThomas Gleixner <tglx@linutronix.de>
Wed, 22 Aug 2007 21:01:37 +0000 (14:01 -0700)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Thu, 23 Aug 2007 02:52:45 +0000 (19:52 -0700)
commit179394af7a2baa1d0a3cb1670075310d72247d38
treef15d4ad366b1bfa7787d6a6a809816f507c4a23a
parent928923c76b393e38e5ba1d47e843e208ceef6cf9
posix-timers: fix deletion race

timer_delete does:
lock_timer();
timer->it_process = NULL;
unlock_timer();
release_posix_timer();

timer->it_process is checked in lock_timer() to prevent access to a
timer, which is on the way to be deleted, but the check happens after
idr_lock is dropped. This allows release_posix_timer() to delete the
timer before the lock code can check the timer:

  CPU 0 CPU 1

  lock_timer();
  timer->it_process = NULL;
  unlock_timer();
lock_timer()
spin_lock(idr_lock);
timer = idr_find();
spin_lock(timer->lock);
spin_unlock(idr_lock);
  release_posix_timer();
spin_lock(idr_lock);
idr_remove(timer);
spin_unlock(idr_lock);
free_timer(timer);
if (timer->......)

Change the locking to prevent this.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/posix-timers.c