Commit eb9abcff authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Luis Henriques

locking/rtmutex: Avoid a NULL pointer dereference on deadlock

commit 8d1e5a1a 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 397335f0 ("rtmutex: Fix
deadlock detector for real") or commit 3d5c9340 ("rtmutex:
Handle deadlock detection smarter").
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1424187823-19600-1-git-send-email-bigeasy@linutronix.deSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent dae27fb6
......@@ -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);
}
......
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