On Tue, Aug 24, 2021 at 10:00:44PM +0800, kernel test robot wrote: > > > Greeting, > > FYI, we noticed the following commit (built with gcc-9): > > commit: c0afb0ffc06e6b4e492a3b711f1fb32074f9949c ("locking/ww_mutex: Gather mutex_waiter initialization") Fixed by... commit b857174e68e26f9c4f0796971e11eb63ad5a3eb6 Author: Sebastian Andrzej Siewior Date: Thu Aug 19 21:30:30 2021 +0200 locking/ww_mutex: Initialize waiter.ww_ctx properly The consolidation of the debug code for mutex waiter intialization sets waiter::ww_ctx to a poison value unconditionally. For regular mutexes this is intended to catch the case where waiter_ww_ctx is dereferenced accidentally. For ww_mutex the poison value has to be overwritten either with a context pointer or NULL for ww_mutexes without context. The rework broke this as it made the store conditional on the context pointer instead of the argument which signals whether ww_mutex code should be compiled in or optiized out. As a result waiter::ww_ctx ends up with the poison pointer for contextless ww_mutexes which causes a later dereference of the poison pointer because it is != NULL. Use the build argument instead so for ww_mutex the poison value is always overwritten. Fixes: c0afb0ffc06e6 ("locking/ww_mutex: Gather mutex_waiter initialization") Reported-by: Guenter Roeck Suggested-by: Peter Zijlstra Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210819193030.zpwrpvvrmy7xxxiy@linutronix.de diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 3a65bf4bacfd..d456579d0952 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -618,7 +618,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas debug_mutex_lock_common(lock, &waiter); waiter.task = current; - if (ww_ctx) + if (use_ww_ctx) waiter.ww_ctx = ww_ctx; lock_contended(&lock->dep_map, ip);