From: Alex Elder <elder@inktank.com>
Date: Fri, 31 May 2013 22:40:45 +0000 (-0500)
Subject: rbd: use rwsem to protect header updates
X-Git-Tag: v3.11-rc1~69^2~22
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cfbf6377b696d88461eef6966bef9e6184111183;p=pandora-kernel.git

rbd: use rwsem to protect header updates

Updating an image header needs to be protected to ensure it's
done consistently.  However distinct headers can be updated
concurrently without a problem.  Instead of using the global
control lock to serialize headder updates, just rely on the header
semaphore.  (It's already used, this just moves it out to cover
a broader section of the code.)

That leaves the control mutex protecting only the creation of rbd
clients, so rename it.

This resolves:
    http://tracker.ceph.com/issues/5222

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
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