Subject: [PATCH 01/16] softirq: Make serving softirqs a task flag
From: Sebastian Andrzej Siewior <[email-masked]>
To: Steven Rostedt <[email-masked]>
Cc: [email-masked], [email-masked], Carsten Emde <[email-masked]>, Thomas Gleixner <[email-masked]>, Sebastian Andrzej Siewior <[email-masked]>
Date: Wed, 13 Feb 2013 17:11:56 +0100
List-Id: <linux-rt-users.vger.kernel.org>

From: Thomas Gleixner <[email-masked]>

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

Signed-off-by: Thomas Gleixner <[email-masked]>
[bigeasy@linutronix: different PF_IN_SOFTIRQ bit]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 include/linux/sched.h |    1 +
 kernel/softirq.c      |   20 +++-----------------
 2 files changed, 4 insertions(+), 17 deletions(-)

Index: linux-3.2.39-rt59/include/linux/sched.h
===================================================================
--- linux-3.2.39-rt59.orig/include/linux/sched.h
+++ linux-3.2.39-rt59/include/linux/sched.h
@@ -1832,6 +1832,7 @@ extern void thread_group_times(struct ta
 /*
  * Per process flags
  */
+#define PF_IN_SOFTIRQ	0x00000001	/* Task is serving softirq */
 #define PF_STARTING	0x00000002	/* being created */
 #define PF_EXITING	0x00000004	/* getting shut down */
 #define PF_EXITPIDONE	0x00000008	/* pi exit done on shut down */
Index: linux-3.2.39-rt59/kernel/softirq.c
===================================================================
--- linux-3.2.39-rt59.orig/kernel/softirq.c
+++ linux-3.2.39-rt59/kernel/softirq.c
@@ -383,7 +383,6 @@ static inline void ksoftirqd_clr_sched_p
  * 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--;
 }