From: Sebastian Andrzej Siewior Date: Tue, 17 Feb 2015 15:43:43 +0000 (+0100) Subject: locking/rtmutex: Avoid a NULL pointer dereference on deadlock X-Git-Tag: v3.16.35~2698 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=eb9abcff096d2b1d89cbf9d968714c339b6f94c3;p=thirdparty%2Fkernel%2Fstable.git locking/rtmutex: Avoid a NULL pointer dereference on deadlock commit 8d1e5a1a1ccf5ae9d8a5a0ee7960202ccb0c5429 upstream. With task_blocks_on_rt_mutex() returning early -EDEADLK we never add the waiter to the waitqueue. Later, we try to remove it via remove_waiter() and go boom in rt_mutex_top_waiter() because rb_entry() gives a NULL pointer. ( Tested on v3.18-RT where rtmutex is used for regular mutex and I tried to get one twice in a row. ) Not sure when this started but I guess 397335f004f4 ("rtmutex: Fix deadlock detector for real") or commit 3d5c9340d194 ("rtmutex: Handle deadlock detection smarter"). Signed-off-by: Sebastian Andrzej Siewior Acked-by: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1424187823-19600-1-git-send-email-bigeasy@linutronix.de Signed-off-by: Ingo Molnar [ luis: backported to 3.16: adjusted context ] Signed-off-by: Luis Henriques --- diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index fc605941b9b89..f9878d16b80b3 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -936,7 +936,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, set_current_state(TASK_RUNNING); if (unlikely(ret)) { - remove_waiter(lock, &waiter); + if (rt_mutex_has_waiters(lock)) + remove_waiter(lock, &waiter); rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter); }