[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>

1 files changed, 11 insertions, 4 deletions

diff --git a/fs/dlm/config.c b/fs/dlm/config.c
index 822abdcd1434..5a3d390cc826 100644
--- a/fs/dlm/config.c
+++ b/fs/dlm/config.c
@@ -748,9 +748,16 @@ 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)
@@ -776,20 +783,20 @@ 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;
 }