Snapshot Cleaner not Working with inode_cache

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I've encountered an issue where the space from previously deleted
snapshots is not being freed up by the cleaner thread.

I'm only encountering this issue when I mount with the inode_cache option.

I've reproduced this on a 3.7.9 kernel merged with the latest
for-linus branch.  No additional patches are involved.  My testing
partition is 16 GB.

There is nothing in dmesg indicating any issues.

A simple manual test can reproduce the issue on my box

(1)  Format a fresh, scratch btrfs partition (it would probably work
with an existing test partition, but I always like to test things that
seem broken on a scratch partition).
(2)  Mount partition (my options are -o
compress-force=lzo,inode_cache).  My mount command was:
mount -o compress-force=lzo,inode_cache /dev/sda7 /mnt/benchmark/
(3)  Make a subvolume:  cd /mnt/<device>; btrfs su create test1
(4)  Untar kernel sources to the subvolume:  cd test1; tar -xpf
<path/to/kernel/source/tarball>
I believe anything you use to populate the subvolume is sufficient.
(5)  Make a note of the disk usage:  df -T /mnt/<device>
(6)  Remove the subvolume:  cd ..; btrfs su delete test1
(7)  Wait 2 minutes, and notice that the space has not been freed up.
I've waited much longer, but I forget the exact timeout on the cleaner
thread.
df -T /mnt/<device>

If I unmount and remount the partition with the same mount options,
the cleaner will begin to correctly free the space.

I've never used the inode_cache option before, so I'll try a few other
kernels to see if this is a regression.
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