From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 22 Aug 2007 21:01:37 +0000 (-0700)
Subject: posix-timers: fix deletion race
X-Git-Tag: v2.6.23-rc4~60
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=179394af7a2baa1d0a3cb1670075310d72247d38;p=pandora-kernel.git

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>
---

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