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Date:	Wed, 15 May 2013 18:08:07 -0700
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	akpm@...ux-foundation.org
Cc:	torvalds@...ux-foundation.org, riel@...hat.com,
	linux-kernel@...r.kernel.org,
	Davidlohr Bueso <davidlohr.bueso@...com>
Subject: [PATCH 08/11] 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@...com>
---
 ipc/msg.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index 9ff295b..2d89b00 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -547,17 +547,25 @@ 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;
@@ -566,8 +574,6 @@ 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;
@@ -577,7 +583,8 @@ 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;
@@ -589,7 +596,7 @@ static int msgctl_nolock(struct ipc_namespace *ns, int msqid,
 
 	return err;
 out_unlock:
-	msg_unlock(msq);
+	rcu_read_unlock();
 	return err;
 }
 
-- 
1.7.11.7

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