Comment # 5 on bug 933427 from Martin Pluskal

Hmm when btrfs balance was running on this fs, it seem that kernel crashed, and
after reboot mount failed: http://paste.opensuse.org/view/raw/14449084
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[  389.619563] kernel BUG at ../fs/btrfs/extent-tree.c:2248!
[  389.620180] ------------[ cut here ]------------
[  389.620199] WARNING: CPU: 2 PID: 628 at ../fs/btrfs/delayed-ref.c:475
update_existing_ref+0x18d/0x1e0 [btrfs]()
[  389.620206] Modules linked in: btrfs xor raid6_pq ata_generic raid0 raid1
md_mod pata_atiixp ohci_pci radeon sr_mod cdrom firewire_ohci i2c_algo_bit
drm_kms_helper firewire_core crc_itu_t ttm drm r8169 mii sg
[  389.620208] CPU: 2 PID: 628 Comm: mount Tainted: G        W      
4.0.5-1-desktop #1
[  389.620209] Hardware name: System manufacturer System Product Name/M4A79
Deluxe, BIOS 4101    04/13/2011
[  389.620210]  0000000000000000 ffffffffa0442a13 ffffffff8167c83a
0000000000000000
[  389.620212]  ffffffff81063bb1 ffff8800cbad4d40 ffff8800cbb31ee8
0000000000000002
[  389.620213]  ffff8800cbb31e80 ffff8801f8d8da68 ffffffffa040b86d
ffff88022496c558
[  389.620213] Call Trace:
[  389.620221]  [<ffffffff8100574c>] dump_trace+0x8c/0x340
[  389.620223]  [<ffffffff81005aa3>] show_stack_log_lvl+0xa3/0x190
[  389.620226]  [<ffffffff81007201>] show_stack+0x21/0x50
[  389.620228]  [<ffffffff8167c83a>] dump_stack+0x47/0x67
[  389.620231]  [<ffffffff81063bb1>] warn_slowpath_common+0x81/0xb0
[  389.620243]  [<ffffffffa040b86d>] update_existing_ref+0x18d/0x1e0 [btrfs]
[  389.620259]  [<ffffffffa040bc17>] add_delayed_tree_ref+0xe7/0x1b0 [btrfs]
[  389.620271]  [<ffffffffa040c824>] btrfs_add_delayed_tree_ref+0x124/0x190
[btrfs]
[  389.620281]  [<ffffffffa03aafd0>] btrfs_free_extent+0xe0/0x140 [btrfs]
[  389.620292]  [<ffffffffa03ab302>] do_walk_down+0x2d2/0x8d0 [btrfs]
[  389.620302]  [<ffffffffa03ab9bc>] walk_down_tree+0xbc/0x100 [btrfs]
[  389.620312]  [<ffffffffa03af371>] btrfs_drop_snapshot+0x401/0x860 [btrfs]
[  389.620326]  [<ffffffffa04138a1>] merge_reloc_roots+0xd1/0x240 [btrfs]
[  389.620338]  [<ffffffffa04146c3>] btrfs_recover_relocation+0x373/0x3d0
[btrfs]
[  389.620348]  [<ffffffffa0394ba1>] btrfs_remount+0x401/0x550 [btrfs]
[  389.620352]  [<ffffffff811d9af6>] do_remount_sb+0x66/0x1f0
[  389.620354]  [<ffffffff811f7bcf>] do_mount+0x6af/0xae0
[  389.620357]  [<ffffffff811f82fc>] SyS_mount+0x8c/0xe0
[  389.620359]  [<ffffffff8168318d>] system_call_fastpath+0x16/0x1b
[  389.620362]  [<00007f30b551c1aa>] 0x7f30b551c1aa
[  389.620362] ---[ end trace 8df34620f5af12f3 ]---
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