From: Mikulas Patocka <mpatocka@redhat.com>
Date: Fri, 13 Sep 2013 21:42:24 +0000 (-0400)
Subject: dm stats: fix possible counter corruption on 32-bit systems
X-Git-Tag: v3.12-rc3~25^2~7
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bbf3f8cbdc139860a14c4fc2bb25432427045aaa;p=pandora-kernel.git

dm stats: fix possible counter corruption on 32-bit systems

There was a deliberate race condition in dm_stat_for_entry() to avoid the
overhead of disabling and enabling interrupts.  The race could result in
some events not being counted on 64-bit architectures.

However, on 32-bit architectures, operations on long long variables are
not atomic, so the race condition could cause the counter to jump by 2^32.
Such jumps could be disruptive, so we need to do proper locking on 32-bit
architectures.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Alasdair G. Kergon <agk@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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