ocfs2: skip locks in the blocked list

A parallel umount on 4 nodes triggered a bug in
dlm_process_recovery_date().  Here's the situation:

Receiving MIG_LOCKRES message, A node processes the locks in migratable
lockres.  It copys lvb from migratable lockres when processing the first
valid lock.

If there is a lock in the blocked list with the EX level, it triggers the
BUG.  Since valid lvbs are set when locks are granted with EX or PR
levels, locks in the blocked list cannot have valid lvbs.  Therefore I
think we should skip the locks in the blocked list.
Signed-off-by: Xuejiufei <xuejiufei@huawei.com>
Signed-off-by: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/dlm/dlmrecovery.c

@@ -1886,6 +1886,13 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
 		if (ml->type == LKM_NLMODE)
 			goto skip_lvb;
 
+		/*
+		 * If the lock is in the blocked list it can't have a valid lvb,
+		 * so skip it
+		 */
+		if (ml->list == DLM_BLOCKED_LIST)
+			goto skip_lvb;
+
 		if (!dlm_lvb_is_empty(mres->lvb)) {
 			if (lksb->flags & DLM_LKSB_PUT_LVB) {
 				/* other node was trying to update