tree 27867ddba8f36d9dc4946c5beee2f18d7be8c861
parent e64860aa05048fa7a8483ca698b17c2caf5625cf
author Josef Bacik <jbacik@fusionio.com> 1342815068 -0400
committer Chris Mason <chris.mason@fusionio.com> 1343075289 -0400

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>