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Patch "ocfs2/dlm: fix deadlock when dispatch assert master" has been added to the 4.1-stable tree

PATCH [email protected] 1 participant 1 message Oct 17, 2015

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This is a note to let you know that I've just added the patch titled

ocfs2/dlm: fix deadlock when dispatch assert master

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ocfs2-dlm-fix-deadlock-when-dispatch-assert-master.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 012572d4fc2e4ddd5c8ec8614d51414ec6cae02a Mon Sep 17 00:00:00 2001

From: Joseph Qi <[email protected]>
Date: Tue, 22 Sep 2015 14:59:20 -0700
Subject: ocfs2/dlm: fix deadlock when dispatch assert master

From: Joseph Qi <[email protected]>

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 <[email protected]>
Cc Joel Becker <[email protected]>
Cc Mark Fasheh <[email protected]>
Cc "Junxiao Bi" <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 fs/ocfs2/dlm/dlmmaster.c   |    9 ++++++---
 fs/ocfs2/dlm/dlmrecovery.c |    8 ++++++--
 2 files changed, 12 insertions(+), 5 deletions(-)
fs/ocfs2/dlm/dlmmaster.c +6 -3
@@ -1439,6 +1439,7 @@ 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;

@@ -1658,15 +1659,18 @@ 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);
+		}
 		spin_unlock(&res->spinlock);
 	} else {
 		if (res)
 			dlm_lockres_put(res);
 	}
 
-	dlm_put(dlm);
+	if (!dispatched)
+		dlm_put(dlm);
 	return response;
 }
 

@@ -2090,7 +2094,6 @@ 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 */
fs/ocfs2/dlm/dlmrecovery.c +6 -2
@@ -1694,6 +1694,7 @@ 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

@@ -1719,8 +1720,10 @@ int dlm_master_requery_handler(struct o2
 				dlm_put(dlm);
 				/* sender will take care of this and retry */
 				return ret;
-			} else
+			} else {
+				dispatched = 1;
 				__dlm_lockres_grab_inflight_worker(dlm, res);
+			}
 			spin_unlock(&res->spinlock);
 		} else {
 			/* put.. incase we are not the master */

@@ -1730,7 +1733,8 @@ int dlm_master_requery_handler(struct o2
 	}
 	spin_unlock(&dlm->spinlock);
 
-	dlm_put(dlm);
+	if (!dispatched)
+		dlm_put(dlm);
 	return master;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/ocfs2-dlm-fix-deadlock-when-dispatch-assert-master.patch