ipc,msg: shorten critical region in msgctl_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>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index f62fa5eed847..de422ff71c87 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -410,11 +410,10 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
         down_write(&msg_ids(ns).rw_mutex);
         rcu_read_lock();
 
-        ipcp = ipcctl_pre_down(ns, &msg_ids(ns), msqid, cmd,
-                               &msqid64.msg_perm, msqid64.msg_qbytes);
+        ipcp = ipcctl_pre_down_nolock(ns, &msg_ids(ns), msqid, cmd,
+                                      &msqid64.msg_perm, msqid64.msg_qbytes);
         if (IS_ERR(ipcp)) {
                 err = PTR_ERR(ipcp);
-                /* the ipc lock is not held upon failure */
                 goto out_unlock1;
         }
 
@@ -422,10 +421,11 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
 
         err = security_msg_queue_msgctl(msq, cmd);
         if (err)
-                goto out_unlock0;
+                goto out_unlock1;
 
         switch (cmd) {
         case IPC_RMID:
+                ipc_lock_object(&msq->q_perm);
                 /* freeque unlocks the ipc object and rcu */
                 freeque(ns, ipcp);
                 goto out_up;
@@ -433,9 +433,10 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
                 if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
                     !capable(CAP_SYS_RESOURCE)) {
                         err = -EPERM;
-                        goto out_unlock0;
+                        goto out_unlock1;
                 }
 
+                ipc_lock_object(&msq->q_perm);
                 err = ipc_update_perm(&msqid64.msg_perm, ipcp);
                 if (err)
                         goto out_unlock0;
@@ -454,6 +455,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
                 break;
         default:
                 err = -EINVAL;
+                goto out_unlock1;
         }
 
 out_unlock0: