ipc,msg: make msgctl_nolock lockless

commit ac0ba20ea6f2201a1589d6dc26ad1a4f0f967bb8 upstream.

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

diff --git a/ipc/msg.c b/ipc/msg.c
index 4e8cf7b..c0fe57c 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;
 }