[  +0,000032] INFO: task btrfs:14183 blocked for more than 120 seconds.
[  +0,000030]       Not tainted 5.5.0-0.bpo.2-amd64 #1 Debian 5.5.17-1~bpo10+1
[  +0,000033] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  +0,000036] btrfs           D    0 14183  14177 0x00004000
[  +0,000002] Call Trace:
[  +0,000003]  ? __schedule+0x2db/0x700
[  +0,000001]  ? mempool_alloc+0x67/0x190
[  +0,000002]  schedule+0x40/0xb0
[  +0,000007]  md_write_start+0x14b/0x220 [md_mod]
[  +0,000002]  ? finish_wait+0x80/0x80
[  +0,000002]  ? finish_wait+0x80/0x80
[  +0,000005]  raid5_make_request+0x83/0xb50 [raid456]
[  +0,000004]  ? bio_add_page+0x39/0x90
[  +0,000023]  ? submit_extent_page+0xd8/0x200 [btrfs]
[  +0,000002]  ? finish_wait+0x80/0x80
[  +0,000002]  ? __blk_queue_split+0x403/0x4c0
[  +0,000002]  ? finish_wait+0x80/0x80
[  +0,000005]  md_handle_request+0x119/0x190 [md_mod]
[  +0,000006]  md_make_request+0x8a/0x190 [md_mod]
[  +0,000003]  generic_make_request+0xcf/0x310
[  +0,000026]  ? btrfs_dev_stat_inc_and_print+0x50/0x50 [btrfs]
[  +0,000001]  submit_bio+0x42/0x1c0
[  +0,000025]  btrfs_map_bio+0x1c0/0x380 [btrfs]
[  +0,000022]  btrfs_submit_bio_hook+0x8c/0x170 [btrfs]
[  +0,000024]  submit_one_bio+0x31/0x50 [btrfs]
[  +0,000024]  extent_writepages+0x6b/0xa0 [btrfs]
[  +0,000002]  do_writepages+0x41/0xd0
[  +0,000024]  ? merge_state.part.43+0x3f/0x160 [btrfs]
[  +0,000002]  __filemap_fdatawrite_range+0xcb/0x100
[  +0,000023]  btrfs_fdatawrite_range+0x1b/0x50 [btrfs]
[  +0,000025]  __btrfs_write_out_cache+0x467/0x4c0 [btrfs]
[  +0,000026]  btrfs_write_out_cache+0x92/0xe0 [btrfs]
[  +0,000023]  btrfs_start_dirty_block_groups+0x270/0x4e0 [btrfs]
[  +0,000023]  btrfs_commit_transaction+0xc5/0xa40 [btrfs]
[  +0,000020]  ? btrfs_record_root_in_trans+0x56/0x60 [btrfs]
[  +0,000021]  ? start_transaction+0xbc/0x4d0 [btrfs]
[  +0,000024]  btrfs_mksubvol+0x4f0/0x530 [btrfs]
[  +0,000026]  btrfs_ioctl_snap_create_transid+0x170/0x180 [btrfs]
[  +0,000024]  btrfs_ioctl_snap_create_v2+0x11c/0x180 [btrfs]
[  +0,000024]  btrfs_ioctl+0x11c2/0x2de0 [btrfs]
[  +0,000004]  ? tomoyo_path_number_perm+0x68/0x1e0
[  +0,000005]  ? do_vfs_ioctl+0xa4/0x680
[  +0,000001]  do_vfs_ioctl+0xa4/0x680
[  +0,000003]  ksys_ioctl+0x60/0x90
[  +0,000001]  __x64_sys_ioctl+0x16/0x20
[  +0,000004]  do_syscall_64+0x52/0x170
[  +0,000002]  entry_SYSCALL_64_after_hwframe+0x44/0xa9