Comment 10 for bug 1454903

I upgraded from kernel 4.4 to 4.8 on 16.04 LTS in the hope the issue would go away. My hang is in btrfs-cleaner, not sure if this is the same bug or not.

This related thread is interesting but does not seem to resolve it: https://patchwork.kernel.org/patch/8284721/

Linux nuc 4.8.0-54-generic #57~16.04.1-Ubuntu SMP Wed May 24 16:22:28 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Jun 19 01:51:14 nuc kernel: INFO: task btrfs-cleaner:408 blocked for more than 120 seconds.
Jun 19 01:51:14 nuc kernel: Not tainted 4.8.0-54-generic #57~16.04.1-Ubuntu
Jun 19 01:51:14 nuc kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jun 19 01:51:14 nuc kernel: btrfs-cleaner D ffff9478128d3d00 0 408 2 0x00000000
Jun 19 01:51:14 nuc kernel: ffff9478128d3d00 ffff9478128d3cc8 ffff94781c2a6ac0 ffff9478137a0000
Jun 19 01:51:14 nuc kernel: ffffffffa4cc7492 ffff9478128d4000 ffff947813e841f0 ffff947813e84000
Jun 19 01:51:14 nuc kernel: ffff947813e841f0 0000000000000001 ffff9478128d3d18 ffffffffa5496045
Jun 19 01:51:14 nuc kernel: Call Trace:
Jun 19 01:51:14 nuc kernel: [<ffffffffa4cc7492>] ? autoremove_wake_function+0x12/0x40
Jun 19 01:51:14 nuc kernel: [<ffffffffa5496045>] schedule+0x35/0x80
Jun 19 01:51:14 nuc kernel: [<ffffffffc079fc73>] wait_current_trans.isra.21+0xd3/0x120 [btrfs]
Jun 19 01:51:14 nuc kernel: [<ffffffffa4cc7480>] ? wake_atomic_t_function+0x60/0x60
Jun 19 01:51:14 nuc kernel: [<ffffffffc07a248f>] start_transaction+0x2cf/0x4c0 [btrfs]
Jun 19 01:51:14 nuc kernel: [<ffffffffc07a2698>] btrfs_start_transaction+0x18/0x20 [btrfs]
Jun 19 01:51:14 nuc kernel: [<ffffffffc0788f72>] btrfs_drop_snapshot+0x4b2/0x800 [btrfs]
Jun 19 01:51:14 nuc kernel: [<ffffffffa5495b87>] ? __schedule+0x307/0x790
Jun 19 01:51:14 nuc kernel: [<ffffffffc07a1624>] btrfs_clean_one_deleted_snapshot+0xb4/0x100 [btrfs]
Jun 19 01:51:14 nuc kernel: [<ffffffffc0797dbd>] cleaner_kthread+0x15d/0x1d0 [btrfs]
Jun 19 01:51:14 nuc kernel: [<ffffffffc0797c60>] ? btrfs_destroy_pinned_extent+0xf0/0xf0 [btrfs]
Jun 19 01:51:14 nuc kernel: [<ffffffffa4ca3fb8>] kthread+0xd8/0xf0
Jun 19 01:51:14 nuc kernel: [<ffffffffa549aa9f>] ret_from_fork+0x1f/0x40
Jun 19 01:51:14 nuc kernel: [<ffffffffa4ca3ee0>] ? kthread_create_on_node+0x1e0/0x1e0