From 6f008e72cd111a119b5d8de8c5438d892aae99eb Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 12 Mar 2014 13:24:42 +0100 Subject: locking/mutex: Fix debug checks OK, so commit: 1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock") generates this boot warning when CONFIG_DEBUG_MUTEXES=y: WARNING: CPU: 0 PID: 139 at /usr/src/linux-2.6/kernel/locking/mutex-debug.c:82 debug_mutex_unlock+0x155/0x180() DEBUG_LOCKS_WARN_ON(lock->owner != current) And that makes sense, because as soon as we release the lock a new owner can come in... One would think that !__mutex_slowpath_needs_to_unlock() implementations suffer the same, but for DEBUG we fall back to mutex-null.h which has an unconditional 1 for that. The mutex debug code requires the mutex to be unlocked after doing the debug checks, otherwise it can find inconsistent state. Reported-by: Ingo Molnar Signed-off-by: Peter Zijlstra Cc: jason.low2@hp.com Link: http://lkml.kernel.org/r/20140312122442.GB27965@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/locking/mutex-debug.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'kernel/locking/mutex-debug.c') diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index faf6f5b53e7..e1191c996c5 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -83,6 +83,12 @@ void debug_mutex_unlock(struct mutex *lock) DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next); mutex_clear_owner(lock); + + /* + * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug + * mutexes so that we can do it here after we've verified state. + */ + atomic_set(&lock->count, 1); } void debug_mutex_init(struct mutex *lock, const char *name, -- cgit v1.2.3-70-g09d2 From a227960fe0cafcc229a8d6bb8b454a3a0b33719d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 10 Apr 2014 16:15:59 +0200 Subject: locking/mutex: Fix debug_mutexes debug_mutex_unlock() would bail when !debug_locks and forgets to actually unlock. Reported-by: "Michael L. Semon" Reported-by: "Kirill A. Shutemov" Reported-by: Valdis Kletnieks Fixes: 6f008e72cd11 ("locking/mutex: Fix debug checks") Tested-by: Dave Jones Cc: Jason Low Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20140410141559.GE13658@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/locking/mutex-debug.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) (limited to 'kernel/locking/mutex-debug.c') diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index e1191c996c5..5cf6731b98e 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -71,18 +71,17 @@ void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter, void debug_mutex_unlock(struct mutex *lock) { - if (unlikely(!debug_locks)) - return; + if (likely(debug_locks)) { + DEBUG_LOCKS_WARN_ON(lock->magic != lock); - DEBUG_LOCKS_WARN_ON(lock->magic != lock); + if (!lock->owner) + DEBUG_LOCKS_WARN_ON(!lock->owner); + else + DEBUG_LOCKS_WARN_ON(lock->owner != current); - if (!lock->owner) - DEBUG_LOCKS_WARN_ON(!lock->owner); - else - DEBUG_LOCKS_WARN_ON(lock->owner != current); - - DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next); - mutex_clear_owner(lock); + DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next); + mutex_clear_owner(lock); + } /* * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug -- cgit v1.2.3-70-g09d2