[PATCH 3.2 087/107] ocfs2/dlm: fix deadlock when dispatch assert master

[Ben Hutchings]

3.2.72-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Joseph Qi <joseph.qi@xxxxxxxxxx>

commit 012572d4fc2e4ddd5c8ec8614d51414ec6cae02a 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@xxxxxxxxxx>
Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Cc: Mark Fasheh <mfasheh@xxxxxxxx>
Cc: "Junxiao Bi" <junxiao.bi@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -1411,6 +1411,7 @@ int dlm_master_request_handler(struct o2
 	int found, ret;
 	int set_maybe;
 	int dispatch_assert = 0;
+	int dispatched = 0;
 
 	if (!dlm_grab(dlm))
 		return DLM_MASTER_RESP_NO;
@@ -1617,13 +1618,16 @@ send_response:
 			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);
 	}
 
-	dlm_put(dlm);
+	if (!dispatched)
+		dlm_put(dlm);
 	return response;
 }
 
@@ -2041,7 +2045,6 @@ int dlm_dispatch_assert_master(struct dl
 
 
 	/* 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 */
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -1689,6 +1689,7 @@ int dlm_master_requery_handler(struct o2
 	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 o2
 				mlog_errno(-ENOMEM);
 				/* retry!? */
 				BUG();
+			} else {
+				dispatched = 1;
 			}
 		} else /* put.. incase we are not the master */
 			dlm_lockres_put(res);
@@ -1717,7 +1720,8 @@ int dlm_master_requery_handler(struct o2
 	}
 	spin_unlock(&dlm->spinlock);
 
-	dlm_put(dlm);
+	if (!dispatched)
+		dlm_put(dlm);
 	return master;
 }
 

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