linux-kernel - [PATCH RFC tip/core/rcu 28/28] rcu: Fix idle-task checks

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Date:	Wed,  2 Nov 2011 13:30:49 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	patches@...aro.org, "Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC tip/core/rcu 28/28] rcu: Fix idle-task checks

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

RCU has traditionally relied on idle_cpu() to determine whether a given
CPU is running in the context of an idle task, but recent changes have
invalidated this approach.  This commit therefore switches from idle_cpu
to "current->pid != 0".

Reported-by: Wu Fengguang <fengguang.wu@...el.com>
Suggested-by: Carsten Emde <C.Emde@...dl.org>
Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Acked-by: Steven Rostedt <rostedt@...dmis.org>
Tested-by: Wu Fengguang <fengguang.wu@...el.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutiny.c |    4 ++--
 kernel/rcutree.c |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index f4e7bc3..35f8a07 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -65,7 +65,7 @@ static void rcu_idle_enter_common(long long oldval)
 		return;
 	}
 	RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
-	if (!idle_cpu(smp_processor_id())) {
+	if (current->pid != 0) {
 		struct task_struct *idle = idle_task(smp_processor_id());
 
 		RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
@@ -119,7 +119,7 @@ static void rcu_idle_exit_common(long long oldval)
 		return;
 	}
 	RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
-	if (!idle_cpu(smp_processor_id())) {
+	if (!current->pid != 0) {
 		struct task_struct *idle = idle_task(smp_processor_id());
 
 		RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 3d7b474..414af68 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -355,7 +355,7 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
 		return;
 	}
 	trace_rcu_dyntick("Start", oldval, rdtp->dynticks_nesting);
-	if (!idle_cpu(smp_processor_id())) {
+	if (current->pid != 0) {
 		struct task_struct *idle = idle_task(smp_processor_id());
 
 		trace_rcu_dyntick("Error on entry: not idle task",
@@ -449,7 +449,7 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
 	smp_mb__after_atomic_inc();  /* See above. */
 	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
 	trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
-	if (!idle_cpu(smp_processor_id())) {
+	if (current->pid != 0) {
 		struct task_struct *idle = idle_task(smp_processor_id());
 
 		trace_rcu_dyntick("Error on exit: not idle task",
-- 
1.7.3.2

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