[3.16.y-ckt stable] Patch "ocfs2/dlm: fix deadlock when dispatch assert master" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ocfs2/dlm: fix deadlock when dispatch assert master

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 7d70db1c5e9ecb60dbffeb4d9313b60fde0d777f Mon Sep 17 00:00:00 2001
From: Joseph Qi <joseph.qi at huawei.com>
Date: Tue, 22 Sep 2015 14:59:20 -0700
Subject: ocfs2/dlm: fix deadlock when dispatch assert master

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 at huawei.com>
Cc: Joel Becker <jlbec at evilplan.org>
Cc: Mark Fasheh <mfasheh at suse.com>
Cc: "Junxiao Bi" <junxiao.bi at oracle.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/ocfs2/dlm/dlmmaster.c   | 9 ++++++---
 fs/ocfs2/dlm/dlmrecovery.c | 8 ++++++--
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 7b9f96899812..189e7e1b7144 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -1450,6 +1450,7 @@ 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;
@@ -1656,14 +1657,17 @@ send_response:
 			mlog(ML_ERROR, "failed to dispatch assert master work\n");
 			response = DLM_MASTER_RESP_ERROR;
 			dlm_lockres_put(res);
-		} else
+		} else {
+			dispatched = 1;
 			dlm_lockres_grab_inflight_worker(dlm, res);
+		}
 	} else {
 		if (res)
 			dlm_lockres_put(res);
 	}

-	dlm_put(dlm);
+	if (!dispatched)
+		dlm_put(dlm);
 	return response;
 }

@@ -2083,7 +2087,6 @@ 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 */
diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index 45067faf5695..5084ce856879 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -1687,6 +1687,7 @@ 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
@@ -1708,15 +1709,18 @@ int dlm_master_requery_handler(struct o2net_msg *msg, u32 len, void *data,
 				mlog_errno(-ENOMEM);
 				/* retry!? */
 				BUG();
-			} else
+			} else {
+				dispatched = 1;
 				__dlm_lockres_grab_inflight_worker(dlm, res);
+			}
 		} else /* put.. incase we are not the master */
 			dlm_lockres_put(res);
 		spin_unlock(&res->spinlock);
 	}
 	spin_unlock(&dlm->spinlock);

-	dlm_put(dlm);
+	if (!dispatched)
+		dlm_put(dlm);
 	return master;
 }