md: enhance checking in md_check_recovery()

For md_check_recovery():

1) if 'MD_RECOVERY_RUNING' is not set, register new sync_thread.
2) if 'MD_RECOVERY_RUNING' is set:
 a) if 'MD_RECOVERY_DONE' is not set, don't do anything, wait for
   md_do_sync() to be done.
 b) if 'MD_RECOVERY_DONE' is set, unregister sync_thread. Current code
   expects that sync_thread is not NULL, otherwise new sync_thread will
   be registered, which will corrupt the array.

Make sure md_check_recovery() won't register new sync_thread if
'MD_RECOVERY_RUNING' is still set, and a new WARN_ON_ONCE() is added for
the above corruption,

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230529132037.2124527-7-yukuai1@huaweicloud.com

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e0d8e751a78289c8e385eddc1b325aea213bca3b..320d71537359ac963c743df2e865fc81762cfa26 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9388,16 +9388,24 @@ void md_check_recovery(struct mddev *mddev)
                if (mddev->sb_flags)
                        md_update_sb(mddev, 0);
 
-               if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
-                   !test_bit(MD_RECOVERY_DONE, &mddev->recovery)) {
-                       /* resync/recovery still happening */
-                       clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
-                       goto unlock;
-               }
-               if (mddev->sync_thread) {
+               /*
+                * Never start a new sync thread if MD_RECOVERY_RUNNING is
+                * still set.
+                */
+               if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
+                       if (!test_bit(MD_RECOVERY_DONE, &mddev->recovery)) {
+                               /* resync/recovery still happening */
+                               clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+                               goto unlock;
+                       }
+
+                       if (WARN_ON_ONCE(!mddev->sync_thread))
+                               goto unlock;
+
                        md_reap_sync_thread(mddev);
                        goto unlock;
                }
+
                /* Set RUNNING before clearing NEEDED to avoid
                 * any transients in the value of "sync_action".
                 */