From: David Teigland <teigland@redhat.com>
Date: Fri, 1 Aug 2008 11:10:14 -0500
Subject: [dlm] fix a couple of races
Message-id: 20080801161013.GB26413@redhat.com
O-Subject: [RHEL5.3 PATCH] dlm: fix a couple of races
Bugzilla: 457569
RH-Acked-by: Steven Whitehouse <swhiteho@redhat.com>
RH-Acked-by: Bob Peterson <rpeterso@redhat.com>

bz 457569 dlm get_comm() uses NULL pointer

brew build including this patch
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1418645

upstream commit:

commit 3168b0780d06ace875696f8a648d04d6089654e5
Author: Satyam Sharma <ssatyam@cse.iitk.ac.in>
Date:   Tue May 8 09:18:58 2007 +0100

    [DLM] fix a couple of races

    Fix two races in fs/dlm/config.c:

    (1) Grab the configfs subsystem semaphore before calling
    config_group_find_obj() in get_space(). This solves a potential race
    between get_space() and concurrent mkdir(2) or rmdir(2).

    (2) Grab a reference on the found config_item _while_ holding the configfs
    subsystem semaphore in get_comm(), and not after it. This solves a
    potential race between get_comm() and concurrent rmdir(2).

    Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>
    Signed-off-by: David Teigland <teigland@redhat.com>
    Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --git a/fs/dlm/config.c b/fs/dlm/config.c
index 3711548..5069b2c 100644
--- a/fs/dlm/config.c
+++ b/fs/dlm/config.c
@@ -754,9 +754,16 @@ static ssize_t node_weight_write(struct node *nd, const char *buf, size_t len)
 
 static struct space *get_space(char *name)
 {
+	struct config_item *i;
+
 	if (!space_list)
 		return NULL;
-	return to_space(config_group_find_obj(space_list, name));
+
+	down(&space_list->cg_subsys->su_sem);
+	i = config_group_find_obj(space_list, name);
+	up(&space_list->cg_subsys->su_sem);
+
+	return to_space(i);
 }
 
 static void put_space(struct space *sp)
@@ -782,20 +789,20 @@ static struct comm *get_comm(int nodeid, struct sockaddr_storage *addr)
 			if (cm->nodeid != nodeid)
 				continue;
 			found = 1;
+			config_item_get(i);
 			break;
 		} else {
 			if (!cm->addr_count ||
 			    memcmp(cm->addr[0], addr, sizeof(*addr)))
 				continue;
 			found = 1;
+			config_item_get(i);
 			break;
 		}
 	}
 	up(&clusters_root.subsys.su_sem);
 
-	if (found)
-		config_item_get(i);
-	else
+	if (!found)
 		cm = NULL;
 	return cm;
 }