ocfs2/dlm: fix deadlock when dispatch assert master

commit 012572d4 upstream.

The order of the following three spinlocks should be:
dlm_domain_lock < dlm_ctxt->spinlock < dlm_lock_resource->spinlock

But dlm_dispatch_assert_master() is called while holding
dlm_ctxt->spinlock and dlm_lock_resource->spinlock, and then it calls
dlm_grab() which will take dlm_domain_lock.

Once another thread (for example, dlm_query_join_handler) has already
taken dlm_domain_lock, and tries to take dlm_ctxt->spinlock deadlock
happens.
Signed-off-by: Joseph Qi <joseph.qi@huawei.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: "Junxiao Bi" <junxiao.bi@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/ocfs2/dlm/dlmmaster.c

@@ -1411,6 +1411,7 @@ int dlm_master_request_handler(struct o2net_msg *msg, u32 len, void *data,
 	int found, ret;
 	int set_maybe;
 	int dispatch_assert = 0;
+	int dispatched = 0;
 
 	if (!dlm_grab(dlm))
 		return DLM_MASTER_RESP_NO;
@@ -1617,12 +1618,15 @@ int dlm_master_request_handler(struct o2net_msg *msg, u32 len, void *data,
 			mlog(ML_ERROR, "failed to dispatch assert master work\n");
 			response = DLM_MASTER_RESP_ERROR;
 			dlm_lockres_put(res);
+		} else {
+			dispatched = 1;
 		}
 	} else {
 		if (res)
 			dlm_lockres_put(res);
 	}
 
+	if (!dispatched)
 		dlm_put(dlm);
 	return response;
 }
@@ -2041,7 +2045,6 @@ int dlm_dispatch_assert_master(struct dlm_ctxt *dlm,
 
 
 	/* queue up work for dlm_assert_master_worker */
-	dlm_grab(dlm);  /* get an extra ref for the work item */
 	dlm_init_work_item(dlm, item, dlm_assert_master_worker, NULL);
 	item->u.am.lockres = res; /* already have a ref */
 	/* can optionally ignore node numbers higher than this node */

fs/ocfs2/dlm/dlmrecovery.c

@@ -1689,6 +1689,7 @@ int dlm_master_requery_handler(struct o2net_msg *msg, u32 len, void *data,
 	unsigned int hash;
 	int master = DLM_LOCK_RES_OWNER_UNKNOWN;
 	u32 flags = DLM_ASSERT_MASTER_REQUERY;
+	int dispatched = 0;
 
 	if (!dlm_grab(dlm)) {
 		/* since the domain has gone away on this
@@ -1710,6 +1711,8 @@ int dlm_master_requery_handler(struct o2net_msg *msg, u32 len, void *data,
 				mlog_errno(-ENOMEM);
 				/* retry!? */
 				BUG();
+			} else {
+				dispatched = 1;
 			}
 		} else /* put.. incase we are not the master */
 			dlm_lockres_put(res);
@@ -1717,6 +1720,7 @@ int dlm_master_requery_handler(struct o2net_msg *msg, u32 len, void *data,
 	}
 	spin_unlock(&dlm->spinlock);
 
+	if (!dispatched)
 		dlm_put(dlm);
 	return master;
 }