md-cluster: fix no recovery job when adding/re-adding a disk

The commit db5e653d ("md: delay choosing sync action to
md_start_sync()") delays the start of the sync action. In a
clustered environment, this will cause another node to first
activate the spare disk and skip recovery. As a result, no
nodes will perform recovery when a disk is added or re-added.

Before db5e653d:

```
   node1                                node2
----------------------------------------------------------------
md_check_recovery
 + md_update_sb
 |  sendmsg: METADATA_UPDATED
 + md_choose_sync_action           process_metadata_update
 |  remove_and_add_spares           //node1 has not finished adding
 + call mddev->sync_work            //the spare disk:do nothing

md_start_sync
 starts md_do_sync

md_do_sync
 + grabbed resync_lockres:DLM_LOCK_EX
 + do syncing job

md_check_recovery
 sendmsg: METADATA_UPDATED
                                 process_metadata_update
                                   //activate spare disk

                                 ... ...

                                 md_do_sync
                                  waiting to grab resync_lockres:EX
```

After db5e653d:

(note: if 'cmd:idle' sets MD_RECOVERY_INTR after md_check_recovery
starts md_start_sync, setting the INTR action will exacerbate the
delay in node1 calling the md_do_sync function.)

```
   node1                                node2
----------------------------------------------------------------
md_check_recovery
 + md_update_sb
 |  sendmsg: METADATA_UPDATED
 + calls mddev->sync_work         process_metadata_update
                                   //node1 has not finished adding
                                   //the spare disk:do nothing

md_start_sync
 + md_choose_sync_action
 |  remove_and_add_spares
 + calls md_do_sync

md_check_recovery
 md_update_sb
  sendmsg: METADATA_UPDATED
                                  process_metadata_update
                                    //activate spare disk

  ... ...                         ... ...

                                  md_do_sync
                                   + grabbed resync_lockres:EX
                                   + raid1_sync_request skip sync under
				     conf->fullsync:0
md_do_sync
 1. waiting to grab resync_lockres:EX
 2. when node1 could grab EX lock,
    node1 will skip resync under recovery_offset:MaxSector
```

How to trigger:

```(commands @node1)
 # to easily watch the recovery status
echo 2000 > /proc/sys/dev/raid/speed_limit_max
ssh root@node2 "echo 2000 > /proc/sys/dev/raid/speed_limit_max"

mdadm -CR /dev/md0 -l1 -b clustered -n 2 /dev/sda /dev/sdb --assume-clean
ssh root@node2 mdadm -A /dev/md0 /dev/sda /dev/sdb
mdadm --manage /dev/md0 --fail /dev/sda --remove /dev/sda
mdadm --manage /dev/md0 --add /dev/sdc

=== "cat /proc/mdstat" on both node, there are no recovery action. ===
```

How to fix:

because md layer code logic is hard to restore for speeding up sync job
on local node, we add new cluster msg to pending the another node to
active disk.
Signed-off-by: Heming Zhao <heming.zhao@suse.com>
Reviewed-by: Su Yue <glass.su@suse.com>
Acked-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240709104120.22243-2-heming.zhao@suse.com

drivers/md/md-cluster.c

@@ -57,6 +57,7 @@ struct resync_info {
 #define		MD_CLUSTER_ALREADY_IN_CLUSTER		6
 #define		MD_CLUSTER_PENDING_RECV_EVENT		7
 #define 	MD_CLUSTER_HOLDING_MUTEX_FOR_RECVD		8
+#define		MD_CLUSTER_WAITING_FOR_SYNC		9
 
 struct md_cluster_info {
 	struct mddev *mddev; /* the md device which md_cluster_info belongs to */
@@ -92,6 +93,7 @@ struct md_cluster_info {
 	sector_t sync_hi;
 };
 
+/* For compatibility, add the new msg_type at the end. */
 enum msg_type {
 	METADATA_UPDATED = 0,
 	RESYNCING,
@@ -101,6 +103,7 @@ enum msg_type {
 	BITMAP_NEEDS_SYNC,
 	CHANGE_CAPACITY,
 	BITMAP_RESIZE,
+	RESYNCING_START,
 };
 
 struct cluster_msg {
@@ -461,6 +464,7 @@ static void process_suspend_info(struct mddev *mddev,
 		clear_bit(MD_RESYNCING_REMOTE, &mddev->recovery);
 		remove_suspend_info(mddev, slot);
 		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+		clear_bit(MD_CLUSTER_WAITING_FOR_SYNC, &cinfo->state);
 		md_wakeup_thread(mddev->thread);
 		return;
 	}
@@ -531,6 +535,7 @@ static int process_add_new_disk(struct mddev *mddev, struct cluster_msg *cmsg)
 		res = -1;
 	}
 	clear_bit(MD_CLUSTER_WAITING_FOR_NEWDISK, &cinfo->state);
+	set_bit(MD_CLUSTER_WAITING_FOR_SYNC, &cinfo->state);
 	return res;
 }
 
@@ -599,6 +604,9 @@ static int process_recvd_msg(struct mddev *mddev, struct cluster_msg *msg)
 	case CHANGE_CAPACITY:
 		set_capacity_and_notify(mddev->gendisk, mddev->array_sectors);
 		break;
+	case RESYNCING_START:
+		clear_bit(MD_CLUSTER_WAITING_FOR_SYNC, &mddev->cluster_info->state);
+		break;
 	case RESYNCING:
 		set_bit(MD_RESYNCING_REMOTE, &mddev->recovery);
 		process_suspend_info(mddev, le32_to_cpu(msg->slot),
@@ -1345,6 +1353,23 @@ static void resync_info_get(struct mddev *mddev, sector_t *lo, sector_t *hi)
 	spin_unlock_irq(&cinfo->suspend_lock);
 }
 
+static int resync_status_get(struct mddev *mddev)
+{
+	struct md_cluster_info *cinfo = mddev->cluster_info;
+
+	return test_bit(MD_CLUSTER_WAITING_FOR_SYNC, &cinfo->state);
+}
+
+static int resync_start_notify(struct mddev *mddev)
+{
+	struct md_cluster_info *cinfo = mddev->cluster_info;
+	struct cluster_msg cmsg = {0};
+
+	cmsg.type = cpu_to_le32(RESYNCING_START);
+
+	return sendmsg(cinfo, &cmsg, 0);
+}
+
 static int resync_info_update(struct mddev *mddev, sector_t lo, sector_t hi)
 {
 	struct md_cluster_info *cinfo = mddev->cluster_info;
@@ -1579,6 +1604,8 @@ static const struct md_cluster_operations cluster_ops = {
 	.resync_start = resync_start,
 	.resync_finish = resync_finish,
 	.resync_info_update = resync_info_update,
+	.resync_start_notify = resync_start_notify,
+	.resync_status_get = resync_status_get,
 	.resync_info_get = resync_info_get,
 	.metadata_update_start = metadata_update_start,
 	.metadata_update_finish = metadata_update_finish,

drivers/md/md-cluster.h

@@ -14,6 +14,8 @@ struct md_cluster_operations {
 	int (*leave)(struct mddev *mddev);
 	int (*slot_number)(struct mddev *mddev);
 	int (*resync_info_update)(struct mddev *mddev, sector_t lo, sector_t hi);
+	int (*resync_start_notify)(struct mddev *mddev);
+	int (*resync_status_get)(struct mddev *mddev);
 	void (*resync_info_get)(struct mddev *mddev, sector_t *lo, sector_t *hi);
 	int (*metadata_update_start)(struct mddev *mddev);
 	int (*metadata_update_finish)(struct mddev *mddev);

drivers/md/md.c

@@ -8978,7 +8978,8 @@ void md_do_sync(struct md_thread *thread)
 	 * This will mean we have to start checking from the beginning again.
 	 *
 	 */
-
+	if (mddev_is_clustered(mddev))
+		md_cluster_ops->resync_start_notify(mddev);
 	do {
 		int mddev2_minor = -1;
 		mddev->curr_resync = MD_RESYNC_DELAYED;
@@ -9992,8 +9993,18 @@ static void check_sb_changes(struct mddev *mddev, struct md_rdev *rdev)
 			 */
 			if (rdev2->raid_disk == -1 && role != MD_DISK_ROLE_SPARE &&
 			    !(le32_to_cpu(sb->feature_map) &
-			      MD_FEATURE_RESHAPE_ACTIVE)) {
-				rdev2->saved_raid_disk = role;
+			      MD_FEATURE_RESHAPE_ACTIVE) &&
+			    !md_cluster_ops->resync_status_get(mddev)) {
+				/*
+				 * -1 to make raid1_add_disk() set conf->fullsync
+				 * to 1. This could avoid skipping sync when the
+				 * remote node is down during resyncing.
+				 */
+				if ((le32_to_cpu(sb->feature_map)
+				    & MD_FEATURE_RECOVERY_OFFSET))
+					rdev2->saved_raid_disk = -1;
+				else
+					rdev2->saved_raid_disk = role;
 				ret = remove_and_add_spares(mddev, rdev2);
 				pr_info("Activated spare: %pg\n",
 					rdev2->bdev);