linux-kernel - [ 086/120] ia64: Add missing RCU idle APIs on idle loop

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Date:	Thu, 11 Oct 2012 10:00:38 +0900
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>
Subject: [ 086/120] ia64: Add missing RCU idle APIs on idle loop

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

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

From: "Paul E. McKenney" <paul.mckenney@...aro.org>

commit 93482f4ef1093f5961a63359a34612183d6beea0 upstream.

Traditionally, the entire idle task served as an RCU quiescent state.
But when RCU read side critical sections started appearing within the
idle loop, this traditional strategy became untenable.  The fix was to
create new RCU APIs named rcu_idle_enter() and rcu_idle_exit(), which
must be called by each architecture's idle loop so that RCU can tell
when it is safe to ignore a given idle CPU.

Unfortunately, this fix was never applied to ia64, a shortcoming remedied
by this commit.

Reported by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Tested by: Tony Luck <tony.luck@...el.com>
Reviewed-by: Josh Triplett <josh@...htriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/ia64/kernel/process.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -29,6 +29,7 @@
 #include <linux/kdebug.h>
 #include <linux/utsname.h>
 #include <linux/tracehook.h>
+#include <linux/rcupdate.h>

 #include <asm/cpu.h>
 #include <asm/delay.h>
@@ -301,6 +302,7 @@ cpu_idle (void)

 	/* endless idle loop with no priority at all */
 	while (1) {
+		rcu_idle_enter();
 		if (can_do_pal_halt) {
 			current_thread_info()->status &= ~TS_POLLING;
 			/*
@@ -331,6 +333,7 @@ cpu_idle (void)
 			normal_xtp();
 #endif
 		}
+		rcu_idle_exit();
 		schedule_preempt_disabled();
 		check_pgt_cache();
 		if (cpu_is_offline(cpu))

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