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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 <bigeasy@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1424187823-19600-1-git-send-email-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
This commit is contained in:
Sebastian Andrzej Siewior 2015-02-17 16:43:43 +01:00 committed by syphyr
parent 7c4a7bdb1f
commit a1e14bfdfc
1 changed files with 2 additions and 1 deletions
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3
kernel/locking/rtmutex.c
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@ -972,7 +972,8 @@ 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);
}