| From 8d1e5a1a1ccf5ae9d8a5a0ee7960202ccb0c5429 Mon Sep 17 00:00:00 2001 |
| From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| Date: Tue, 17 Feb 2015 16:43:43 +0100 |
| Subject: locking/rtmutex: Avoid a NULL pointer dereference on deadlock |
| |
| From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| |
| 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> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/locking/rtmutex.c | 3 ++- |
| 1 file changed, 2 insertions(+), 1 deletion(-) |
| |
| --- a/kernel/locking/rtmutex.c |
| +++ b/kernel/locking/rtmutex.c |
| @@ -1193,7 +1193,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, |
| 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); |
| } |
| |
