softirq: Consolidate common code in tasklet_[hi]_action()

tasklet_action() + tasklet_hi_action() are almost identical.  Move the
common code from both function into __tasklet_action_common() and let
both functions invoke it with different arguments.

[ bigeasy: Splitted out from RT's "tasklet: Prevent tasklets from going
	   into infinite spin in RT" and added commit message]

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Julia Cartwright <juliac@eso.teric.us>
Link: https://lkml.kernel.org/r/20180227164808.10093-3-bigeasy@linutronix.de

kernel/softirq.c

@@ -490,14 +490,16 @@ void __tasklet_hi_schedule(struct tasklet_struct *t)
 }
 EXPORT_SYMBOL(__tasklet_hi_schedule);
 
-static __latent_entropy void tasklet_action(struct softirq_action *a)
+static void tasklet_action_common(struct softirq_action *a,
+				  struct tasklet_head *tl_head,
+				  unsigned int softirq_nr)
 {
 	struct tasklet_struct *list;
 
 	local_irq_disable();
-	list = __this_cpu_read(tasklet_vec.head);
-	__this_cpu_write(tasklet_vec.head, NULL);
-	__this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
+	list = tl_head->head;
+	tl_head->head = NULL;
+	tl_head->tail = &tl_head->head;
 	local_irq_enable();
 
 	while (list) {
@@ -519,47 +521,21 @@ static __latent_entropy void tasklet_action(struct softirq_action *a)
 
 		local_irq_disable();
 		t->next = NULL;
-		*__this_cpu_read(tasklet_vec.tail) = t;
-		__this_cpu_write(tasklet_vec.tail, &(t->next));
-		__raise_softirq_irqoff(TASKLET_SOFTIRQ);
+		*tl_head->tail = t;
+		tl_head->tail = &t->next;
+		__raise_softirq_irqoff(softirq_nr);
 		local_irq_enable();
 	}
 }
 
-static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
+static __latent_entropy void tasklet_action(struct softirq_action *a)
 {
-	struct tasklet_struct *list;
-
-	local_irq_disable();
-	list = __this_cpu_read(tasklet_hi_vec.head);
-	__this_cpu_write(tasklet_hi_vec.head, NULL);
-	__this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
-	local_irq_enable();
-
-	while (list) {
-		struct tasklet_struct *t = list;
-
-		list = list->next;
-
-		if (tasklet_trylock(t)) {
-			if (!atomic_read(&t->count)) {
-				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
-							&t->state))
-					BUG();
-				t->func(t->data);
-				tasklet_unlock(t);
-				continue;
-			}
-			tasklet_unlock(t);
-		}
+	tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
+}
 
-		local_irq_disable();
-		t->next = NULL;
-		*__this_cpu_read(tasklet_hi_vec.tail) = t;
-		__this_cpu_write(tasklet_hi_vec.tail, &(t->next));
-		__raise_softirq_irqoff(HI_SOFTIRQ);
-		local_irq_enable();
-	}
+static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
+{
+	tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
 }
 
 void tasklet_init(struct tasklet_struct *t,