From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:30:12 -0500
Subject: ipc: Make the ipc code -rt aware

RT serializes the code with the (rt)spinlock but keeps preemption
enabled. Some parts of the code need to be atomic nevertheless.

Protect it with preempt_disable/enable_rt pairts.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 ipc/msg.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -188,6 +188,12 @@ static void expunge_all(struct msg_queue
 	struct msg_receiver *msr, *t;
 
 	list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
+		/*
+		 * Make sure that the wakeup doesnt preempt
+		 * this CPU prematurely. (on PREEMPT_RT)
+		 */
+		preempt_disable_rt();
+
 		msr->r_msg = NULL; /* initialize expunge ordering */
 		wake_up_process(msr->r_tsk);
 		/*
@@ -198,6 +204,8 @@ static void expunge_all(struct msg_queue
 		 */
 		smp_mb();
 		msr->r_msg = ERR_PTR(res);
+
+		preempt_enable_rt();
 	}
 }
 
@@ -574,6 +582,11 @@ static inline int pipelined_send(struct
 		if (testmsg(msg, msr->r_msgtype, msr->r_mode) &&
 		    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk,
 					       msr->r_msgtype, msr->r_mode)) {
+			/*
+			 * Make sure that the wakeup doesnt preempt
+			 * this CPU prematurely. (on PREEMPT_RT)
+			 */
+			preempt_disable_rt();
 
 			list_del(&msr->r_list);
 			if (msr->r_maxsize < msg->m_ts) {
@@ -595,12 +608,13 @@ static inline int pipelined_send(struct
 				 */
 				smp_mb();
 				msr->r_msg = msg;
+				preempt_enable_rt();
 
 				return 1;
 			}
+			preempt_enable_rt();
 		}
 	}
-
 	return 0;
 }