[PATCH 5.10 120/798] ocfs2: cluster: fix o2hb_dependent_users leak on pin failure

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joseph Qi <joseph.qi@linux.alibaba.com>

commit 12c2ab42dbe227956c765e2674364bfca5de0533 upstream.

In o2hb_region_inc_user(), o2hb_dependent_users is incremented
unconditionally before calling o2hb_region_pin().  If the pin fails, the
counter is never decremented and any partially-pinned regions are never
unpinned, since the caller does not call o2hb_region_dec_user() on error.

The leaked counter causes subsequent o2hb_region_inc_user() calls to skip
pinning entirely (the > 1 check), leaving heartbeat regions unprotected.

Fix by rolling back on failure: call o2hb_region_unpin(NULL) to release
any partially-pinned regions and decrement o2hb_dependent_users to restore
the pre-increment state.

Link: https://lore.kernel.org/20260722124933.430554-4-joseph.qi@linux.alibaba.com (local)
Fixes: 58a3158a5d17 ("ocfs2/cluster: Pin/unpin o2hb regions")
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <redacted>
Cc: Changwei Ge <redacted>
Cc: Jun Piao <redacted>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/ocfs2/cluster/heartbeat.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/ocfs2/cluster/heartbeat.c
+++ b/fs/ocfs2/cluster/heartbeat.c

@@ -2444,8 +2444,13 @@ static int o2hb_region_inc_user(const ch
 		goto unlock;
 
 	if (bitmap_weight(o2hb_quorum_region_bitmap,
-			   O2NM_MAX_REGIONS) <= O2HB_PIN_CUT_OFF)
+			  O2NM_MAX_REGIONS) <= O2HB_PIN_CUT_OFF) {
 		ret = o2hb_region_pin(NULL, false);
+		if (ret) {
+			o2hb_region_unpin(NULL);
+			o2hb_dependent_users--;
+		}
+	}
 
 unlock:
 	spin_unlock(&o2hb_live_lock);