Patch "alpha: Add missing RCU idle APIs on idle loop" has been added to the 3.4-stable tree

This is a note to let you know that I've just added the patch titled

alpha: Add missing RCU idle APIs on idle loop

to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alpha-add-missing-rcu-idle-apis-on-idle-loop.patch
and it can be found in the queue-3.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From 4c94cada48f7c660eca582be6032427a5e367117 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <[email protected]>
Date: Wed, 22 Aug 2012 17:27:34 +0200
Subject: alpha: Add missing RCU idle APIs on idle loop

From: Frederic Weisbecker <[email protected]>

commit 4c94cada48f7c660eca582be6032427a5e367117 upstream.

In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode.

This is necessary for RCU to find the quiescent states in idle in order to complete grace periods.

Add this missing pair of calls in the Alpha's idle loop.

---
 arch/alpha/kernel/process.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -28,6 +28,7 @@
 #include <linux/tty.h>
 #include <linux/console.h>
 #include <linux/slab.h>
+#include <linux/rcupdate.h>
 
 #include <asm/reg.h>
 #include <asm/uaccess.h>

@@ -54,8 +55,11 @@ cpu_idle(void)
 		/* FIXME -- EV6 and LCA45 know how to power down
 		   the CPU.  */
 
+		rcu_idle_enter();
 		while (!need_resched())
 			cpu_relax();
+
+		rcu_idle_exit();
 		schedule();
 	}
 }

Patches currently in stable-queue which might be from [email protected] are

queue-3.4/frv-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/cris-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/m68k-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/alpha-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/h8300-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/parisc-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/m32r-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/score-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/mn10300-add-missing-rcu-idle-apis-on-idle-loop.patch queue-3.4/xtensa-add-missing-rcu-idle-apis-on-idle-loop.patch