mutex: Always clear owner field upon mutex_unlock()
Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only cleared iff debug_locks is active. This exposes a race to other users of the field where the mutex->owner may be still set to a stale value, potentially upsetting mutex_spin_on_owner() among others. References: https://bugs.freedesktop.org/show_bug.cgi?id=87955 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Davidlohr Bueso <dave@stgolabs.net> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -80,13 +80,13 @@ void debug_mutex_unlock(struct mutex *lock)
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DEBUG_LOCKS_WARN_ON(lock->owner != current);
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DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
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mutex_clear_owner(lock);
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}
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/*
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* __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug
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* mutexes so that we can do it here after we've verified state.
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*/
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mutex_clear_owner(lock);
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atomic_set(&lock->count, 1);
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}
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