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locking/rt-mutex: avoid a NULL pointer dereference on deadlock 

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 397335f00 ("rtmutex: Fix deadlock
detector for real") or commit 3d5c9340 ("rtmutex: Handle deadlock
detection smarter").

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Sebastian Andrzej Siewior 2015-02-17 16:18:05 +01:00 committed by Alibek Omarov
parent ef453cd0d4
commit 7ffb28ebaa
1 changed files with 2 additions and 1 deletions
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3
kernel/locking/rtmutex.c
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@ -1697,7 +1697,8 @@ 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, chwalk, &waiter);
} else if (ww_ctx) {
ww_mutex_account_lock(lock, ww_ctx);