[PATCH v3 2/3] md-cluster: fix error handling and superblock consistency in update_size

[ghuicao]

From: Cao Guanghui <caoguanghui@xxxxxxxxxx>

update_size() has multiple issues in the revert path when
cluster_check_sync_size() detects that not all nodes have confirmed
the new size:

1. (pre-existing) The return value of resize() is immediately
   overwritten by __sendmsg(), so a resize failure is silently lost.

2. (pre-existing) The on-disk superblock still retains the new size
   from the earlier md_update_sb() call.  Other nodes re-read it and
   adopt the new size while the initiator runs with the reverted old
   size.

3. (pre-existing) The function returns void, so callers cannot detect
   failures.

Fix all of the above by:
- Using a separate variable for __sendmsg result so resize failure
  is not overwritten
- Calling md_update_sb() after unlock_comm() to write the reverted
  size back to disk.  This must be outside the locked section because
  md_update_sb() internally acquires MD_CLUSTER_SEND_LOCK via
  metadata_update_start(), which would self-deadlock if already held.
- Changing return type from void to int with proper error codes
  (-EIO for lock failure, -ENODEV for no device, ret for others)

Fixes: 818da59f97d6 ("md-cluster: add the support for resize")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Cao Guanghui <caoguanghui@xxxxxxxxxx>
---
 drivers/md/md-cluster.c | 28 +++++++++++++++++++++++++---
 drivers/md/md-cluster.h |  2 +-
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
--- a/drivers/md/md-cluster.c
+++ b/drivers/md/md-cluster.c
@@ -1302,18 +1302,19 @@ static int cluster_check_sync_size(struct mddev *mddev)
  *    let other nodes to perform it. If one node can't update sync_size
  *    accordingly, we need to revert to previous value.
  */
-static void update_size(struct mddev *mddev, sector_t old_dev_sectors)
+static int update_size(struct mddev *mddev, sector_t old_dev_sectors)
 {
 	struct md_cluster_info *cinfo = mddev->cluster_info;
+	bool reverted = false;
 	struct cluster_msg cmsg;
 	struct md_rdev *rdev;
-	int ret = 0;
+	int ret = 0, msg_ret = 0;
 	int raid_slot = -1;
 
 	md_update_sb(mddev, 1);
 	if (lock_comm(cinfo, 1)) {
 		pr_err("%s: lock_comm failed\n", __func__);
-		return;
+		return -EIO;
 	}
 
 	memset(&cmsg, 0, sizeof(cmsg));
@@ -1335,12 +1336,12 @@ static int update_size(struct mddev *mddev, sector_t old_dev_sectors)
 			pr_err("%s:%d: failed to send METADATA_UPDATED msg\n",
 			       __func__, __LINE__);
 			unlock_comm(cinfo);
-			return;
+			return ret;
 		}
 	} else {
 		pr_err("md-cluster: No good device id found to send\n");
 		unlock_comm(cinfo);
-		return;
+		return -ENODEV;
 	}
 
 	/*
@@ -1359,12 +1360,28 @@ static int update_size(struct mddev *mddev, sector_t old_dev_sectors)
 	} else {
 		/* revert to previous sectors */
 		ret = mddev->pers->resize(mddev, old_dev_sectors);
-		ret = __sendmsg(cinfo, &cmsg);
 		if (ret)
+			pr_err("%s:%d: failed to revert array size\n",
+			       __func__, __LINE__);
+		reverted = true;
+		msg_ret = __sendmsg(cinfo, &cmsg);
+		if (msg_ret) {
 			pr_err("%s:%d: failed to send METADATA_UPDATED msg\n",
 			       __func__, __LINE__);
+			if (!ret)
+				ret = msg_ret;
+		}
 	}
 	unlock_comm(cinfo);
+
+	if (reverted)
+		/* Update on-disk superblock to match reverted in-memory
+		 * size. Must be after unlock_comm() to avoid self-deadlock
+		 * since md_update_sb() acquires the cluster send lock.
+		 */
+		md_update_sb(mddev, 1);
+
+	return ret;
 }
 
 static int resync_start(struct mddev *mddev)
diff --git a/drivers/md/md-cluster.h b/drivers/md/md-cluster.h
--- a/drivers/md/md-cluster.h
+++ b/drivers/md/md-cluster.h
@@ -34,7 +34,7 @@ struct md_cluster_operations {
 	int (*resize_bitmaps)(struct mddev *mddev, sector_t newsize, sector_t oldsize);
 	int (*lock_all_bitmaps)(struct mddev *mddev);
 	void (*unlock_all_bitmaps)(struct mddev *mddev);
-	void (*update_size)(struct mddev *mddev, sector_t old_dev_sectors);
+	int (*update_size)(struct mddev *mddev, sector_t old_dev_sectors);
 };
 
 extern int md_setup_cluster(struct mddev *mddev, int nodes);
-- 
2.34.1