linux-kernel - [ 36/69] ipc,msg: introduce lockless functions to obtain the ipc object

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Message-Id: <20131016174317.287427785@linuxfoundation.org>
Date:	Wed, 16 Oct 2013 10:44:45 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Davidlohr Bueso <davidlohr.bueso@...com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Galbraith <efault@....de>
Subject: [ 36/69] ipc,msg: introduce lockless functions to obtain the ipc object

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Davidlohr Bueso <davidlohr.bueso@...com>

commit a5001a0d9768568de5d613c3b3a5b9c7721299da upstream.

Add msq_obtain_object() and msq_obtain_object_check(), which will allow
us to get the ipc object without acquiring the lock.  Just as with
semaphores, these functions are basically wrappers around
ipc_obtain_object*().

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@...com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: Rik van Riel <riel@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 ipc/msg.c |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -166,6 +166,27 @@ static inline struct msg_queue *msg_lock
 	return container_of(ipcp, struct msg_queue, q_perm);
 }
 
+static inline struct msg_queue *msq_obtain_object(struct ipc_namespace *ns, int id)
+{
+	struct kern_ipc_perm *ipcp = ipc_obtain_object(&msg_ids(ns), id);
+
+	if (IS_ERR(ipcp))
+		return ERR_CAST(ipcp);
+
+	return container_of(ipcp, struct msg_queue, q_perm);
+}
+
+static inline struct msg_queue *msq_obtain_object_check(struct ipc_namespace *ns,
+							int id)
+{
+	struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&msg_ids(ns), id);
+
+	if (IS_ERR(ipcp))
+		return ERR_CAST(ipcp);
+
+	return container_of(ipcp, struct msg_queue, q_perm);
+}
+
 static inline void msg_rmid(struct ipc_namespace *ns, struct msg_queue *s)
 {
 	ipc_rmid(&msg_ids(ns), &s->q_perm);


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