linux-kernel - [08/59] ocfs2/dlm: fix a dead lock

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Date:	Tue, 24 Aug 2010 15:24:20 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Wengang Wang <wen.gang.wang@...cle.com>,
	Joel Becker <joel.becker@...cle.com>
Subject: [08/59] ocfs2/dlm: fix a dead lock

2.6.32-stable review patch.  If anyone has any objections, please let us know.

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

From: Wengang Wang <wen.gang.wang@...cle.com>

commit 6d98c3ccb52f692f1a60339dde7c700686a5568b upstream.

When we have to take both dlm->master_lock and lockres->spinlock,
take them in order

lockres->spinlock and then dlm->master_lock.

The patch fixes a violation of the rule.
We can simply move taking dlm->master_lock to where we have dropped res->spinlock
since when we access res->state and free mle memory we don't need master_lock's
protection.

Signed-off-by: Wengang Wang <wen.gang.wang@...cle.com>
Signed-off-by: Joel Becker <joel.becker@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/ocfs2/dlm/dlmmaster.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -3046,8 +3046,6 @@ int dlm_migrate_request_handler(struct o
 	/* check for pre-existing lock */
 	spin_lock(&dlm->spinlock);
 	res = __dlm_lookup_lockres(dlm, name, namelen, hash);
-	spin_lock(&dlm->master_lock);
-
 	if (res) {
 		spin_lock(&res->spinlock);
 		if (res->state & DLM_LOCK_RES_RECOVERING) {
@@ -3065,14 +3063,15 @@ int dlm_migrate_request_handler(struct o
 		spin_unlock(&res->spinlock);
 	}
 
+	spin_lock(&dlm->master_lock);
 	/* ignore status.  only nonzero status would BUG. */
 	ret = dlm_add_migration_mle(dlm, res, mle, &oldmle,
 				    name, namelen,
 				    migrate->new_master,
 				    migrate->master);
 
-unlock:
 	spin_unlock(&dlm->master_lock);
+unlock:
 	spin_unlock(&dlm->spinlock);
 
 	if (oldmle) {


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