From: Nick Piggin <npiggin@gmail.com>
Date: Fri, 25 Feb 2011 22:44:26 +0000 (-0800)
Subject: aio: fix rcu ioctx lookup
X-Git-Tag: v2.6.38-rc7~18
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3bd9a5d734c7cc7533b27abf451416c7f50095a7;p=pandora-kernel.git

aio: fix rcu ioctx lookup

aio-dio-invalidate-failure GPFs in aio_put_req from io_submit.

lookup_ioctx doesn't implement the rcu lookup pattern properly.
rcu_read_lock does not prevent refcount going to zero, so we might take
a refcount on a zero count ioctx.

Fix the bug by atomically testing for zero refcount before incrementing.

[jack@suse.cz: added comment into the code]
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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