Revert "Revert "ANDROID: softirq: defer softirq processing to ksoftirqd if CPU is busy with RT""

This reverts commit 28768780d4, as the
merge conflicts have been resolved.

Bug: 168521633
Change-Id: I9828d641e92e40a798e899b60aba83dbc59675bb
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
[satyap@codeaurora.org: trivial merge conflict resolution.]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>
[elavila: Port to mainline, squash with bugfix]
Signed-off-by: J. Avila <elavila@google.com>
[ashayj@codeaurora.org: trivial merge conflict resolution.]
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>
Signed-off-by: Shaleen Agrawal <shalagra@codeaurora.org>

include/linux/sched.h

@@ -1798,6 +1798,16 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
 
 extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
 extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed);
+
+#ifdef CONFIG_RT_SOFTINT_OPTIMIZATION
+extern bool cpupri_check_rt(void);
+#else
+static inline bool cpupri_check_rt(void)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_SMP
 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);

kernel/sched/cpupri.c

@@ -355,3 +355,16 @@ void cpupri_cleanup(struct cpupri *cp)
 	for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
 		free_cpumask_var(cp->pri_to_cpu[i].mask);
 }
+
+#ifdef CONFIG_RT_SOFTINT_OPTIMIZATION
+/*
+ * cpupri_check_rt - check if CPU has a RT task
+ * should be called from rcu-sched read section.
+ */
+bool cpupri_check_rt(void)
+{
+	int cpu = raw_smp_processor_id();
+
+	return cpu_rq(cpu)->rd->cpupri.cpu_to_pri[cpu] > CPUPRI_NORMAL;
+}
+#endif

kernel/softirq.c

@@ -522,6 +522,17 @@ static inline bool lockdep_softirq_start(void) { return false; }
 static inline void lockdep_softirq_end(bool in_hardirq) { }
 #endif
 
+static inline __u32 softirq_deferred_for_rt(__u32 *pending)
+{
+	__u32 deferred = 0;
+
+	if (cpupri_check_rt()) {
+		deferred = *pending & LONG_SOFTIRQ_MASK;
+		*pending &= ~LONG_SOFTIRQ_MASK;
+	}
+	return deferred;
+}
+
 asmlinkage __visible void __softirq_entry __do_softirq(void)
 {
 	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
@@ -529,6 +540,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	int max_restart = MAX_SOFTIRQ_RESTART;
 	struct softirq_action *h;
 	bool in_hardirq;
+	__u32 deferred;
 	__u32 pending;
 	int softirq_bit;
 
@@ -541,13 +553,14 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 
 	pending = local_softirq_pending();
 
+	deferred = softirq_deferred_for_rt(&pending);
 	softirq_handle_begin();
 	in_hardirq = lockdep_softirq_start();
 	account_softirq_enter(current);
 
 restart:
 	/* Reset the pending bitmask before enabling irqs */
-	set_softirq_pending(0);
+	set_softirq_pending(deferred);
 	__this_cpu_write(active_softirqs, pending);
 
 	local_irq_enable();
@@ -586,14 +599,17 @@ restart:
 	local_irq_disable();
 
 	pending = local_softirq_pending();
+	deferred = softirq_deferred_for_rt(&pending);
+
 	if (pending) {
 		if (time_before(jiffies, end) && !need_resched() &&
 		    --max_restart)
 			goto restart;
-
-		wakeup_softirqd();
 	}
 
+	if (pending | deferred)
+		wakeup_softirqd();
+
 	account_softirq_exit(current);
 	lockdep_softirq_end(in_hardirq);
 	softirq_handle_end();