On Thu, Feb 1, 2024 at 5:30 PM Yu Kuai [off-list ref] wrote:

From: Yu Kuai <redacted>

mddev_suspend() never stop sync_thread, hence it doesn't make sense to
ignore suspended array in md_check_recovery(), which might cause
sync_thread can't be unregistered.

After commit f52f5c71f3d4 ("md: fix stopping sync thread"), following
hang can be triggered by test shell/integrity-caching.sh:

Hi Kuai

After applying this patch, it's still stuck at mddev_suspend. Maybe
the deadlock can be fixed by other patches from the patch set. But
this patch can't fix this issue. If so, the comment is not right.

1) suspend the array:
raid_postsuspend
 mddev_suspend

2) stop the array:
raid_dtr
 md_stop
  __md_stop_writes
   stop_sync_thread
    set_bit(MD_RECOVERY_INTR, &mddev->recovery);
    md_wakeup_thread_directly(mddev->sync_thread);
    wait_event(..., !test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))

3) sync thread done:
md_do_sync
 set_bit(MD_RECOVERY_DONE, &mddev->recovery);
 md_wakeup_thread(mddev->thread);

4) daemon thread can't unregister sync thread:
md_check_recovery
 if (mddev->suspended)
   return; -> return directly
 md_read_sync_thread
 clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
 -> MD_RECOVERY_RUNNING can't be cleared, hence step 2 hang;

I add some debug logs when stopping dmraid with lvremove command. The
step you mentioned are sequential but not async. The process is :
dev_remove->dm_destroy->__dm_destroy->dm_table_postsuspend_targets(raid_postsuspend)
-> dm_table_destroy(raid_dtr). It looks like mddev_suspend is waiting
for active_io to be zero.

Best Regards
Xiao