Issue

• Two hosts that make use of btrfs and its snapshot feature crash often the message "kernel BUG at fs/btrfs/extent_io.c:4041". Probably the crashes happen in time correlation with new snapshots.
• kernel crash in btrfs_release_extent_buffer_page with the following oops from btrfs-endio-wri

kernel BUG at fs/btrfs/extent_io.c:4041!
invalid opcode: 0000 [#1] SMP 
...
Pid: 39533, comm: btrfs-endio-wri Tainted: G           -- ------------  T 2.6.32-573.1.1.el6.x86_64 #1 Dell Inc. PowerEdge R720/0020HJ
RIP: 0010:[<ffffffffa03e9550>]  [<ffffffffa03e9550>] btrfs_release_extent_buffer_page.clone.0+0x90/0x120 [btrfs]
...
Call Trace:
 [<ffffffffa03e9a9a>] release_extent_buffer+0x4a/0xe0 [btrfs]
 [<ffffffffa03e9c9c>] free_extent_buffer+0x3c/0xa0 [btrfs]
 [<ffffffffa03a0c81>] btrfs_release_path+0x31/0x90 [btrfs]
 [<ffffffffa03bc4fa>] btrfs_csum_file_blocks+0x49a/0x6d0 [btrfs]
 [<ffffffffa03d4314>] ? insert_reserved_file_extent.clone.0+0x94/0x270 [btrfs]
 [<ffffffffa03c8eb9>] add_pending_csums+0x49/0x70 [btrfs]
 [<ffffffffa03d4755>] btrfs_finish_ordered_io+0x265/0x3f0 [btrfs]
 [<ffffffff81089c10>] ? process_timeout+0x0/0x10
 [<ffffffffa03d48f5>] finish_ordered_fn+0x15/0x20 [btrfs]
 [<ffffffffa03f8a02>] worker_loop+0x142/0x550 [btrfs]
 [<ffffffffa03f88c0>] ? worker_loop+0x0/0x550 [btrfs]
 [<ffffffff810a101e>] kthread+0x9e/0xc0
 [<ffffffff8100c28a>] child_rip+0xa/0x20
 [<ffffffff810a0f80>] ? kthread+0x0/0xc0
 [<ffffffff8100c280>] ? child_rip+0x0/0x20
Code: 00 00 48 83 eb 01 4c 8b 24 d8 4d 85 e4 75 24 0f 1f 40 00 48 85 db 75 e3 5b 41 5c 41 5d 41 5e c9 c3 66 2e 0f 1f 84 00 00 00 00 00 <0f> 0b eb fe 0f 1f 40 00 45 84 f6 75 13 4c 89 e7 e8 8b 48 d5 e0 
RIP  [<ffffffffa03e9550>] btrfs_release_extent_buffer_page.clone.0+0x90/0x120 [btrfs]
 RSP <ffff881f9cb87c10>