linux-kernel - [RFC PATCH 29/30] softirq: Make softirq processing softinterruptible

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Date:   Thu, 11 Oct 2018 01:12:16 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Subject: [RFC PATCH 29/30] softirq: Make softirq processing softinterruptible

From: Frederic Weisbecker <fweisbec@...il.com>

Make do_softirq() re-entrant and allow a vector, being either processed
or disabled, to be interrupted by another vector. This way a vector
won't be able to monopolize the CPU for a long while at the expense of
the others that may rely on some predictable latency, especially on
softirq disabled sections that used to disable all vectors.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: David S. Miller <davem@...emloft.net>
Cc: Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/softirq.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 457bf60..f4cb1ea 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -195,7 +195,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt, unsigned int bh)
 	if (cnt)
 		preempt_count_sub(cnt - 1);
 
-	if (unlikely(!in_interrupt() && local_softirq_pending())) {
+	if (unlikely(!in_irq() && (local_softirq_pending() & local_softirq_enabled()))) {
 		/*
 		 * Run softirq if any pending. And do it in its own stack
 		 * as we may be calling this deep in a task call stack already.
@@ -387,7 +387,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	lockdep_softirq_end(in_hardirq);
 	account_irq_exit_time(current);
 	local_bh_exit();
-	WARN_ON_ONCE(in_interrupt());
+	WARN_ON_ONCE(in_irq());
 	current_restore_flags(old_flags, PF_MEMALLOC);
 }
 
@@ -396,12 +396,12 @@ asmlinkage __visible void do_softirq(void)
 	__u32 pending;
 	unsigned long flags;
 
-	if (in_interrupt())
+	if (in_irq())
 		return;
 
 	local_irq_save(flags);
 
-	pending = local_softirq_pending();
+	pending = local_softirq_pending() & local_softirq_enabled();
 
 	if (pending && !ksoftirqd_running(pending))
 		do_softirq_own_stack();
@@ -432,7 +432,7 @@ void irq_enter(void)
 
 static inline void invoke_softirq(void)
 {
-	if (ksoftirqd_running(local_softirq_pending()))
+	if (ksoftirqd_running(local_softirq_pending() & local_softirq_enabled()))
 		return;
 
 	if (!force_irqthreads) {
@@ -481,7 +481,7 @@ void irq_exit(void)
 #endif
 	account_irq_exit_time(current);
 	preempt_count_sub(HARDIRQ_OFFSET);
-	if (!in_interrupt() && local_softirq_pending())
+	if (!in_irq() && (local_softirq_pending() & local_softirq_enabled()))
 		invoke_softirq();
 
 	tick_irq_exit();
@@ -712,13 +712,13 @@ void __init softirq_init(void)
 
 static int ksoftirqd_should_run(unsigned int cpu)
 {
-	return local_softirq_pending();
+	return local_softirq_pending() & local_softirq_enabled();
 }
 
 static void run_ksoftirqd(unsigned int cpu)
 {
 	local_irq_disable();
-	if (local_softirq_pending()) {
+	if (local_softirq_pending() & local_softirq_enabled()) {
 		/*
 		 * We can safely run softirq on inline stack, as we are not deep
 		 * in the task stack here.
-- 
2.7.4