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: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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