ipc,msg: shorten critical region in msgsnd
Davidlohr Bueso [Mon, 8 Jul 2013 23:01:17 +0000 (16:01 -0700)]
commit 3dd1f784ed6603d7ab1043e51e6371235edf2313 upstream.

do_msgsnd() is another function that does too many things with the ipc
object lock acquired.  Take it only when needed when actually updating
msq.

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>

ipc/msg.c

index c0fe57c..1505053 100644 (file)
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -698,10 +698,11 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
        msg->m_type = mtype;
        msg->m_ts = msgsz;
 
-       msq = msg_lock_check(ns, msqid);
+       rcu_read_lock();
+       msq = msq_obtain_object_check(ns, msqid);
        if (IS_ERR(msq)) {
                err = PTR_ERR(msq);
-               goto out_free;
+               goto out_unlock1;
        }
 
        for (;;) {
@@ -709,11 +710,11 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
 
                err = -EACCES;
                if (ipcperms(ns, &msq->q_perm, S_IWUGO))
-                       goto out_unlock_free;
+                       goto out_unlock1;
 
                err = security_msg_queue_msgsnd(msq, msg, msgflg);
                if (err)
-                       goto out_unlock_free;
+                       goto out_unlock1;
 
                if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
                                1 + msq->q_qnum <= msq->q_qbytes) {
@@ -723,32 +724,41 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
                /* queue full, wait: */
                if (msgflg & IPC_NOWAIT) {
                        err = -EAGAIN;
-                       goto out_unlock_free;
+                       goto out_unlock1;
                }
+
+               ipc_lock_object(&msq->q_perm);
                ss_add(msq, &s);
 
                if (!ipc_rcu_getref(msq)) {
                        err = -EIDRM;
-                       goto out_unlock_free;
+                       goto out_unlock0;
                }
 
-               msg_unlock(msq);
+               ipc_unlock_object(&msq->q_perm);
+               rcu_read_unlock();
                schedule();
 
-               ipc_lock_by_ptr(&msq->q_perm);
+               rcu_read_lock();
+               ipc_lock_object(&msq->q_perm);
+
                ipc_rcu_putref(msq);
                if (msq->q_perm.deleted) {
                        err = -EIDRM;
-                       goto out_unlock_free;
+                       goto out_unlock0;
                }
+
                ss_del(&s);
 
                if (signal_pending(current)) {
                        err = -ERESTARTNOHAND;
-                       goto out_unlock_free;
+                       goto out_unlock0;
                }
+
+               ipc_unlock_object(&msq->q_perm);
        }
 
+       ipc_lock_object(&msq->q_perm);
        msq->q_lspid = task_tgid_vnr(current);
        msq->q_stime = get_seconds();
 
@@ -764,9 +774,10 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
        err = 0;
        msg = NULL;
 
-out_unlock_free:
-       msg_unlock(msq);
-out_free:
+out_unlock0:
+       ipc_unlock_object(&msq->q_perm);
+out_unlock1:
+       rcu_read_unlock();
        if (msg != NULL)
                free_msg(msg);
        return err;