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=87955Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk> Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org> Acked-by: NDavidlohr 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.ukSigned-off-by: NIngo Molnar <mingo@kernel.org>
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