ipc,shm: shorten critical region in shmctl_down

Instead of holding the ipc lock for the entire function, use the
ipcctl_pre_down_nolock and only acquire the lock for specific commands:
RMID and SET.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 216ae727a936..22cffd78dbb1 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -780,11 +780,10 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
         down_write(&shm_ids(ns).rw_mutex);
         rcu_read_lock();
 
-        ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
-                               &shmid64.shm_perm, 0);
+        ipcp = ipcctl_pre_down_nolock(ns, &shm_ids(ns), shmid, cmd,
+                                      &shmid64.shm_perm, 0);
         if (IS_ERR(ipcp)) {
                 err = PTR_ERR(ipcp);
-                /* the ipc lock is not held upon failure */
                 goto out_unlock1;
         }
 
@@ -792,14 +791,16 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
 
         err = security_shm_shmctl(shp, cmd);
         if (err)
-                goto out_unlock0;
+                goto out_unlock1;
 
         switch (cmd) {
         case IPC_RMID:
+                ipc_lock_object(&shp->shm_perm);
                 /* do_shm_rmid unlocks the ipc object and rcu */
                 do_shm_rmid(ns, ipcp);
                 goto out_up;
         case IPC_SET:
+                ipc_lock_object(&shp->shm_perm);
                 err = ipc_update_perm(&shmid64.shm_perm, ipcp);
                 if (err)
                         goto out_unlock0;
@@ -807,6 +808,7 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
                 break;
         default:
                 err = -EINVAL;
+                goto out_unlock1;
         }
 
 out_unlock0: