1 files changed, 13 insertions, 3 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index d20cc25c5bdf..8cf1cf3d5bec 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -63,8 +63,6 @@ static struct ipc_ids init_shm_ids;
         ((struct shmid_kernel*)ipc_lock(&shm_ids(ns),id))
 #define shm_unlock(shp)                 \
         ipc_unlock(&(shp)->shm_perm)
-#define shm_get(ns, id)                 \
-        ((struct shmid_kernel*)ipc_get(&shm_ids(ns),id))
 #define shm_buildid(ns, id, seq)        \
         ipc_buildid(&shm_ids(ns), id, seq)
 
@@ -563,7 +561,19 @@ static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
                 struct shmid_kernel *shp;
                 struct inode *inode;
 
-                shp = shm_get(ns, next_id);
+                /*
+                 * idr_find() is called via shm_get(), so with shm_ids.mutex
+                 * locked. Since ipc_addid() is also called with
+                 * shm_ids.mutex down, there is no need to add read barriers
+                 * here to gurantee the writes in ipc_addid() are seen in
+                 * order here (for Alpha).
+                 * However idr_find() itself does not necessary require
+                 * ipc_ids.mutex down. So if idr_find() is used by other
+                 * places without ipc_ids.mutex down, then it needs read
+                 * read memory barriers as ipc_lock() does.
+                 */
+
+                shp = idr_find(&shm_ids(ns).ipcs_idr, next_id);
                 if (shp == NULL)
                         continue;