shm: optimize exit_shm()
We may optimistically check .in_use == 0 without holding the rw_mutex: it's the common case, and if it's zero, there certainly won't be any segments associated with us. After taking the lock, the idr_for_each() will do the right thing, so we could now drop the re-check inside the lock without any real cost. But it won't hurt. Signed-off-by: NVasiliy Kulikov <segoon@openwall.com> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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