ipc,shm: shorten critical region in shmctl_down
Davidlohr Bueso [Wed, 11 Sep 2013 21:26:16 +0000 (14:26 -0700)]
commit 79ccf0f8c8e04e8b9eda6645ba0f63b0915a3075 upstream.

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>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

ipc/shm.c

index 5f106b4..9020ac8 100644 (file)
--- 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: