From: Josef Bacik <jbacik@fusionio.com>
Date: Fri, 20 Jul 2012 20:11:08 +0000 (-0400)
Subject: Btrfs: fix potential race in extent buffer freeing
X-Git-Tag: v3.6-rc1~81^2~9
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=594831c4b232b094d645503ecedec2e35dcebdf3;p=pandora-kernel.git

Btrfs: fix potential race in extent buffer freeing

This sounds sort of impossible but it is the only thing I can think of and
at the very least it is theoretically possible so here it goes.

If we are in try_release_extent_buffer we will check that the ref count on
the extent buffer is 1 and not under IO, and then go down and clear the tree
ref.  If between this check and clearing the tree ref somebody else comes in
and grabs a ref on the eb and the marks it dirty before
try_release_extent_buffer() does it's tree ref clear we can end up with a
dirty eb that will be freed while it is still dirty which will result in a
panic.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
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