CVE-2024-26758

In the Linux kernel, the following vulnerability has been resolved:

md: Don’t ignore suspended array in md_check_recovery()

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:

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.