ocfs2: add spinlock protection when dealing with lockres->purge.

when we check/modify lockres->purge, we should with the protection of lockres->spinlock.
in dlm_purge_lockres(), the checking/modifying is not with the protectin.
this patch fixes it.
Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

fs/ocfs2/dlm/dlmthread.c

@@ -212,14 +212,18 @@ static int dlm_purge_lockres(struct dlm_ctxt *dlm,
 		spin_lock(&dlm->spinlock);
 	}
 
+	spin_lock(&res->spinlock);
 	if (!list_empty(&res->purge)) {
 		mlog(0, "removing lockres %.*s:%p from purgelist, "
 		     "master = %d\n", res->lockname.len, res->lockname.name,
 		     res, master);
 		list_del_init(&res->purge);
+		spin_unlock(&res->spinlock);
 		dlm_lockres_put(res);
 		dlm->purge_count--;
-	}
+	} else
+		spin_unlock(&res->spinlock);
+
 	__dlm_unhash_lockres(res);
 
 	/* lockres is not in the hash now.  drop the flag and wake up