dlm: fix remove member after close call

The idea of commit 63e711b ("fs: dlm: create midcomms nodes when
configure") is to set the midcomms node lifetime when a node joins or
leaves the cluster. Currently we can hit the following warning:

[10844.611495] ------------[ cut here ]------------
[10844.615913] WARNING: CPU: 4 PID: 84304 at fs/dlm/midcomms.c:1263
dlm_midcomms_remove_member+0x13f/0x180 [dlm]

or running in a state where we hit a midcomms node usage count in a
negative value:

[  260.830782] node 2 users dec count -1

The first warning happens when the a specific node does not exists and
it was probably removed but dlm_midcomms_close() which is called when a
node leaves the cluster. The second kernel log message is probably in a
case when dlm_midcomms_addr() is called when a joined the cluster but
due fencing a node leaved the cluster without getting removed from the
lockspace. If the node joins the cluster and it was removed from the
cluster due fencing the first call is to remove the node from lockspaces
triggered by the user space. In both cases if the node wasn't found or
the user count is zero, we should ignore any additional midcomms handling
of dlm_midcomms_remove_member().

Fixes: 63e711b ("fs: dlm: create midcomms nodes when configure")
Signed-off-by: Alexander Aring <[email protected]>
Signed-off-by: David Teigland <[email protected]>

Author: Alexander Aring

fs/dlm/midcomms.c

@@ -1268,12 +1268,23 @@ void dlm_midcomms_remove_member(int nodeid)
 
 	idx = srcu_read_lock(&nodes_srcu);
 	node = nodeid2node(nodeid);
-	if (WARN_ON_ONCE(!node)) {
+	/* in case of dlm_midcomms_close() removes node */
+	if (!node) {
 		srcu_read_unlock(&nodes_srcu, idx);
 		return;
 	}
 
 	spin_lock(&node->state_lock);
+	/* case of dlm_midcomms_addr() created node but
+	 * was not added before because dlm_midcomms_close()
+	 * removed the node
+	 */
+	if (!node->users) {
+		spin_unlock(&node->state_lock);
+		srcu_read_unlock(&nodes_srcu, idx);
+		return;
+	}
+
 	node->users--;
 	pr_debug("node %d users dec count %d\n", nodeid, node->users);