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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 f52f5c71

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

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;

This problem is not just related to dm-raid, fix it by ignoring
suspended array in md_check_recovery(). And follow up patches will
improve dm-raid better to frozen sync thread during suspend.
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Closes: https://lore.kernel.org/all/8fb335e-6d2c-dbb5-d7-ded8db5145a@redhat.com/
Fixes: 68866e42 ("MD: no sync IO while suspended")
Fixes: f52f5c71

 ("md: fix stopping sync thread")
Cc: stable@vger.kernel.org # v6.7+
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240201092559.910982-2-yukuai1@huaweicloud.com