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

[Paul E. McKenney]

From: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>

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@xxxxxxxxx>
Suggested-by: Carsten Emde <C.Emde@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Tested-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 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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