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Sender: Tejun Heo <htejun@gmail.com>
Date: Thu, 15 Feb 2024 15:23:25 -1000
From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
	Naresh Kamboju <naresh.kamboju@linaro.org>,
	Anders Roxell <anders.roxell@linaro.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Valentin Schneider <vschneid@redhat.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH wq/for-6.9] workqueue, irq_work: Build fix for
 !CONFIG_IRQ_WORK
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From 9d6efa8d0dd012db22958a225246812441b25405 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Thu, 15 Feb 2024 15:02:30 -1000

2f34d7337d98 ("workqueue: Fix queue_work_on() with BH workqueues") added
irq_work usage to workqueue; however, it turns out irq_work is actually
optional and the change breaks build on configuration which doesn't have
CONFIG_IRQ_WORK enabled.

Fix build by making workqueue use irq_work only when CONFIG_SMP and enabling
CONFIG_IRQ_WORK when CONFIG_SMP is set. It's reasonable to argue that it may
be better to just always enable it. However, this still saves a small bit of
memory for tiny UP configs and also the least amount of change, so, for now,
let's keep it conditional.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 2f34d7337d98 ("workqueue: Fix queue_work_on() with BH workqueues")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
---
Hello,

As this is breaking build for some configs, I'll apply this to wq/for-6.9.
If there's any objection, please let me know. I'll back out and work on a
different approach.

Thanks.

 init/Kconfig       |  2 ++
 kernel/workqueue.c | 24 +++++++++++++++---------
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 8df18f3a9748..41be05a8ba5e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -107,6 +107,8 @@ config CONSTRUCTORS
 
 config IRQ_WORK
 	bool
+	depends on SMP
+	default y
 
 config BUILDTIME_TABLE_SORT
 	bool
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 04e35dbe6799..6ae441e13804 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1209,6 +1209,20 @@ static struct irq_work *bh_pool_irq_work(struct worker_pool *pool)
 	return &per_cpu(bh_pool_irq_works, pool->cpu)[high];
 }
 
+static void kick_bh_pool(struct worker_pool *pool)
+{
+#ifdef CONFIG_SMP
+	if (unlikely(pool->cpu != smp_processor_id())) {
+		irq_work_queue_on(bh_pool_irq_work(pool), pool->cpu);
+		return;
+	}
+#endif
+	if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
+		raise_softirq_irqoff(HI_SOFTIRQ);
+	else
+		raise_softirq_irqoff(TASKLET_SOFTIRQ);
+}
+
 /**
  * kick_pool - wake up an idle worker if necessary
  * @pool: pool to kick
@@ -1227,15 +1241,7 @@ static bool kick_pool(struct worker_pool *pool)
 		return false;
 
 	if (pool->flags & POOL_BH) {
-		if (likely(pool->cpu == smp_processor_id())) {
-			if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
-				raise_softirq_irqoff(HI_SOFTIRQ);
-			else
-				raise_softirq_irqoff(TASKLET_SOFTIRQ);
-		} else {
-			irq_work_queue_on(bh_pool_irq_work(pool), pool->cpu);
-		}
-
+		kick_bh_pool(pool);
 		return true;
 	}
 
-- 
2.43.2