ipc,msg: make msgctl_nolock lockless

While the INFO cmd doesn't take the ipc lock, the STAT commands do acquire
it unnecessarily.  We can do the permissions and security checks only
holding the rcu lock.

This function now mimics semctl_nolock().

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>

diff --git a/ipc/msg.c b/ipc/msg.c
index c53c1371606441d9b89d463ff60319ae8aa47bae..c218328b59806ff43f8c8762c0bd4806dfc84ac7 100644 (file)
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -545,17 +545,25 @@ static int msgctl_nolock(struct ipc_namespace *ns, int msqid,
                if (!buf)
                        return -EFAULT;
 
+               memset(&tbuf, 0, sizeof(tbuf));
+
+               rcu_read_lock();
                if (cmd == MSG_STAT) {
-                       msq = msg_lock(ns, msqid);
-                       if (IS_ERR(msq))
-                               return PTR_ERR(msq);
+                       msq = msq_obtain_object(ns, msqid);
+                       if (IS_ERR(msq)) {
+                               err = PTR_ERR(msq);
+                               goto out_unlock;
+                       }
                        success_return = msq->q_perm.id;
                } else {
-                       msq = msg_lock_check(ns, msqid);
-                       if (IS_ERR(msq))
-                               return PTR_ERR(msq);
+                       msq = msq_obtain_object_check(ns, msqid);
+                       if (IS_ERR(msq)) {
+                               err = PTR_ERR(msq);
+                               goto out_unlock;
+                       }
                        success_return = 0;
                }
+
                err = -EACCES;
                if (ipcperms(ns, &msq->q_perm, S_IRUGO))
                        goto out_unlock;
@@ -564,8 +572,6 @@ static int msgctl_nolock(struct ipc_namespace *ns, int msqid,
                if (err)
                        goto out_unlock;
 
-               memset(&tbuf, 0, sizeof(tbuf));
-
                kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
                tbuf.msg_stime  = msq->q_stime;
                tbuf.msg_rtime  = msq->q_rtime;
@@ -575,7 +581,8 @@ static int msgctl_nolock(struct ipc_namespace *ns, int msqid,
                tbuf.msg_qbytes = msq->q_qbytes;
                tbuf.msg_lspid  = msq->q_lspid;
                tbuf.msg_lrpid  = msq->q_lrpid;
-               msg_unlock(msq);
+               rcu_read_unlock();
+
                if (copy_msqid_to_user(buf, &tbuf, version))
                        return -EFAULT;
                return success_return;
@@ -587,7 +594,7 @@ static int msgctl_nolock(struct ipc_namespace *ns, int msqid,
 
        return err;
 out_unlock:
-       msg_unlock(msq);
+       rcu_read_unlock();
        return err;
 }