Messages in this thread Patch in this message | | | Date | Thu, 12 Mar 2015 15:21:56 -0400 | From | Steven Rostedt <> | Subject | [PATCH RT 17/36] rt-mutex: avoid a NULL pointer dereference on deadlock |
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3.12.38-rt53-rc1 stable review patch. If anyone has any objections, please let me know.
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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> --- kernel/rtmutex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c index fcaddd510b7a..77f50d221d9c 100644 --- a/kernel/rtmutex.c +++ b/kernel/rtmutex.c @@ -1625,7 +1625,8 @@ 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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