From 8d1e5a1a1ccf5ae9d8a5a0ee7960202ccb0c5429 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 17 Feb 2015 16:43:43 +0100 Subject: locking/rtmutex: 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 397335f004f4 ("rtmutex: Fix deadlock detector for real") or commit 3d5c9340d194 ("rtmutex: Handle deadlock detection smarter"). Signed-off-by: Sebastian Andrzej Siewior Acked-by: Peter Zijlstra Cc: Thomas Gleixner Cc: # for v3.16 and later kernels Link: http://lkml.kernel.org/r/1424187823-19600-1-git-send-email-bigeasy@linutronix.de Signed-off-by: Ingo Molnar --- kernel/locking/rtmutex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/locking/rtmutex.c') diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 3059bc2f022d..e16e5542bf13 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1193,7 +1193,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, ret = __rt_mutex_slowlock(lock, state, timeout, &waiter); if (unlikely(ret)) { - remove_waiter(lock, &waiter); + if (rt_mutex_has_waiters(lock)) + remove_waiter(lock, &waiter); rt_mutex_handle_deadlock(ret, chwalk, &waiter); } -- cgit v1.2.3 From 9d3e2d02f54160725d97f4ab1e1e8de493fbf33a Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Fri, 27 Feb 2015 17:57:09 +0100 Subject: locking/rtmutex: Set state back to running on error The "usual" path is: - rt_mutex_slowlock() - set_current_state() - task_blocks_on_rt_mutex() (ret 0) - __rt_mutex_slowlock() - sleep or not but do return with __set_current_state(TASK_RUNNING) - back to caller. In the early error case where task_blocks_on_rt_mutex() return -EDEADLK we never change the task's state back to RUNNING. I assume this is intended. Without this change after ww_mutex using rt_mutex the selftest passes but later I get plenty of: | bad: scheduling from the idle thread! backtraces. Signed-off-by: Sebastian Andrzej Siewior Acked-by: Mike Galbraith Cc: Linus Torvalds Cc: Maarten Lankhorst Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: afffc6c1805d ("locking/rtmutex: Optimize setting task running after being blocked") Link: http://lkml.kernel.org/r/1425056229-22326-4-git-send-email-bigeasy@linutronix.de Signed-off-by: Ingo Molnar --- kernel/locking/rtmutex.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/locking/rtmutex.c') diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index e16e5542bf13..6357265a31ad 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1193,6 +1193,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, ret = __rt_mutex_slowlock(lock, state, timeout, &waiter); if (unlikely(ret)) { + __set_current_state(TASK_RUNNING); if (rt_mutex_has_waiters(lock)) remove_waiter(lock, &waiter); rt_mutex_handle_deadlock(ret, chwalk, &waiter); -- cgit v1.2.3