Patch "ocfs2: dlm: fix race between purge and get lock resource" has been added to the 4.0-stable tree

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

ocfs2: dlm: fix race between purge and get lock resource

to the 4.0-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-race-between-purge-and-get-lock-resource.patch
and it can be found in the queue-4.0 subdirectory.

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

From: Junxiao Bi <[email protected]>
Date: Tue, 5 May 2015 16:24:02 -0700
Subject: ocfs2: dlm: fix race between purge and get lock resource

From: Junxiao Bi <[email protected]>

commit b1432a2a35565f538586774a03bf277c27fc267d upstream.

There is a race window in dlm_get_lock_resource(), which may return a lock resource which has been purged. This will cause the process to hang forever in dlmlock() as the ast msg can't be handled due to its lock resource not existing.

    dlm_get_lock_resource {
        ...
        spin_lock(&dlm->spinlock);
        tmpres = __dlm_lookup_lockres_full(dlm, lockid, namelen, hash);
        if (tmpres) {
             spin_unlock(&dlm->spinlock);
             >>>>>>>> race window, dlm_run_purge_list() may run and purge
                              the lock resource
             spin_lock(&tmpres->spinlock);
             ...
             spin_unlock(&tmpres->spinlock);
        }
    }

---
 fs/ocfs2/dlm/dlmmaster.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

@@ -757,6 +757,19 @@ lookup:
 	if (tmpres) {
 		spin_unlock(&dlm->spinlock);
 		spin_lock(&tmpres->spinlock);
+
+		/*
+		 * Right after dlm spinlock was released, dlm_thread could have
+		 * purged the lockres. Check if lockres got unhashed. If so
+		 * start over.
+		 */
+		if (hlist_unhashed(&tmpres->hash_node)) {
+			spin_unlock(&tmpres->spinlock);
+			dlm_lockres_put(tmpres);
+			tmpres = NULL;
+			goto lookup;
+		}
+
 		/* Wait on the thread that is mastering the resource */
 		if (tmpres->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
 			__dlm_wait_on_lockres(tmpres);

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

queue-4.0/ocfs2-dlm-fix-race-between-purge-and-get-lock-resource.patch