System hang with raid6 md device deadlock while waiting for bitmap

Issue

• System hang with raid6 md device deadlock while waiting for bitmap:

[1032640.899276] task:kworker/u97:1   state:D stack:    0 pid:1450641 ppid:     2 flags:0x80004080
[1032640.899666] Workqueue: writeback wb_workfn (flush-253:13)
[1032640.900013] Call Trace:
[1032640.900347]  __schedule+0x2d1/0x830
[1032640.900751]  ? blk_flush_plug_list+0xc2/0x100
[1032640.901065]  ? finish_wait+0x80/0x80
[1032640.901414]  schedule+0x35/0xa0
[1032640.901758]  md_bitmap_startwrite+0x16f/0x1e0
[1032640.902065]  ? finish_wait+0x80/0x80
[1032640.902412]  add_stripe_bio+0x4ad/0x7d0 [raid456]
[1032640.902760]  raid5_make_request+0x1d4/0xc00 [raid456]
[1032640.903092]  ? pool_map+0x69/0x90 [dm_thin_pool]
[1032640.903496]  ? linear_map+0x50/0x90 [dm_mod]
[1032640.903906]  ? finish_wait+0x80/0x80
[1032640.904287]  ? finish_wait+0x80/0x80
[1032640.904701]  md_handle_request+0x119/0x190
[1032640.905034]  md_make_request+0x5b/0xb0
[1032640.905478]  generic_make_request+0x25b/0x350
[1032640.905874]  submit_bio+0x3c/0x160
[1032640.906222]  iomap_writepage_map+0x509/0x670
[1032640.906648]  write_cache_pages+0x197/0x420
[1032640.907001]  ? iomap_invalidatepage+0xe0/0xe0
[1032640.907348]  ? skcipher_recvmsg_nokey+0x1f/0x50
[1032640.907744]  iomap_writepages+0x1c/0x40
[1032640.908071]  xfs_vm_writepages+0x7e/0xb0 [xfs]
[1032640.908524]  do_writepages+0xc2/0x1c0
[1032640.908866]  __writeback_single_inode+0x39/0x2f0
[1032640.909214]  writeback_sb_inodes+0x1e6/0x450
[1032640.909598]  __writeback_inodes_wb+0x5f/0xc0
[1032640.909963]  wb_writeback+0x247/0x2e0
[1032640.910369]  ? get_nr_inodes+0x35/0x50
....
[1032640.916428] task:kworker/u96:0   state:D stack:    0 pid:1451365 ppid:     2 flags:0x80004080
[1032640.916793] Workqueue: dm-thin do_worker [dm_thin_pool]
[1032640.917137] Call Trace:
[1032640.917509]  __schedule+0x2d1/0x830
[1032640.917866]  ? finish_wait+0x80/0x80
[1032640.918211]  schedule+0x35/0xa0
[1032640.918571]  md_bitmap_startwrite+0x16f/0x1e0
[1032640.918924]  ? finish_wait+0x80/0x80
[1032640.919224]  add_stripe_bio+0x4ad/0x7d0 [raid456]
[1032640.919623]  raid5_make_request+0x1d4/0xc00 [raid456]
[1032640.919998]  ? pool_map+0x69/0x90 [dm_thin_pool]
[1032640.920401]  ? linear_map+0x50/0x90 [dm_mod]
[1032640.920760]  ? finish_wait+0x80/0x80
[1032640.921082]  ? finish_wait+0x80/0x80
[1032640.921417]  md_handle_request+0x119/0x190
[1032640.921752]  md_make_request+0x5b/0xb0
[1032640.922050]  generic_make_request+0x25b/0x350
[1032640.922444]  ? remap.isra.49+0x57/0xa0 [dm_thin_pool]
[1032640.922799]  inc_remap_and_issue_cell+0xc0/0x100 [dm_thin_pool]
[1032640.923151]  process_prepared_mapping+0xf3/0x1a0 [dm_thin_pool]
[1032640.923543]  process_prepared+0x8f/0xc0 [dm_thin_pool]
[1032640.923922]  do_worker+0x52/0xd0 [dm_thin_pool]
[1032640.924259]  process_one_work+0x1a7/0x360
[1032640.924646]  worker_thread+0x30/0x390
[1032640.924973]  ? create_worker+0x1a0/0x1a0
[1032640.925291]  kthread+0x10a/0x120
[1032640.925695]  ? set_kthread_struct+0x40/0x40
[1032640.926029]  ret_from_fork+0x35/0x40