Messages in this thread Patch in this message |  | | From | Sebastian Andrzej Siewior <> | Subject | [PATCH] locking/rt-mutex: avoid a NULL pointer dereference on deadlock | Date | Tue, 17 Feb 2015 16:43:43 +0100 |
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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").
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/locking/rtmutex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 5906c14a4e64..2f95e56ed33e 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1700,7 +1700,8 @@ 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); -- 2.1.4
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