Subject: softirq: Make serving softirqs a task flag
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 04 Oct 2012 14:30:25 +0100

Avoid the percpu softirq_runner pointer magic by using a task flag.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/sched.h |    1 +
 kernel/softirq.c      |   20 +++-----------------
 2 files changed, 4 insertions(+), 17 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1668,6 +1668,7 @@ extern void thread_group_cputime_adjuste
 /*
  * Per process flags
  */
+#define PF_IN_SOFTIRQ	0x00000001	/* Task is serving softirq */
 #define PF_EXITING	0x00000004	/* getting shut down */
 #define PF_EXITPIDONE	0x00000008	/* pi exit done on shut down */
 #define PF_VCPU		0x00000010	/* I'm a virtual CPU */
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -383,7 +383,6 @@ static void ksoftirqd_clr_sched_params(u
  * On RT we serialize softirq execution with a cpu local lock
  */
 static DEFINE_LOCAL_IRQ_LOCK(local_softirq_lock);
-static DEFINE_PER_CPU(struct task_struct *, local_softirq_runner);
 
 static void __do_softirq_common(int need_rcu_bh_qs);
 
@@ -438,22 +437,9 @@ void _local_bh_enable(void)
 }
 EXPORT_SYMBOL(_local_bh_enable);
 
-/* For tracing */
-int notrace __in_softirq(void)
-{
-	if (__get_cpu_var(local_softirq_lock).owner == current)
-		return __get_cpu_var(local_softirq_lock).nestcnt;
-	return 0;
-}
-
 int in_serving_softirq(void)
 {
-	int res;
-
-	preempt_disable();
-	res = __get_cpu_var(local_softirq_runner) == current;
-	preempt_enable();
-	return res;
+	return current->flags & PF_IN_SOFTIRQ;
 }
 EXPORT_SYMBOL(in_serving_softirq);
 
@@ -471,7 +457,7 @@ static void __do_softirq_common(int need
 	/* Reset the pending bitmask before enabling irqs */
 	set_softirq_pending(0);
 
-	__get_cpu_var(local_softirq_runner) = current;
+	current->flags |= PF_IN_SOFTIRQ;
 
 	lockdep_softirq_enter();
 
@@ -482,7 +468,7 @@ static void __do_softirq_common(int need
 		wakeup_softirqd();
 
 	lockdep_softirq_exit();
-	__get_cpu_var(local_softirq_runner) = NULL;
+	current->flags &= ~PF_IN_SOFTIRQ;
 
 	current->softirq_nestcnt--;
 }