linux-kernel - [PATCH RT] smp: Wake ksoftirqd on PREEMPT_RT instead do

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Message-ID: <20210215181027.mxkzolp3fibfiwvv@linutronix.de>
Date:   Mon, 15 Feb 2021 19:10:27 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH RT] smp: Wake ksoftirqd on PREEMPT_RT instead do_softirq().

The softirq implementation on PREEMPT_RT does not provide do_softirq().
The other user of do_softirq() is replaced with a local_bh_disable()
+ enable() around the possible raise-softirq invocation. This can not be
done here because migration_cpu_stop() is invoked with disabled
preemption.

Wake the softirq thread on PREEMPT_RT if there are any pending softirqs.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/smp.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -450,8 +450,18 @@ void flush_smp_call_function_from_idle(v

 	local_irq_save(flags);
 	flush_smp_call_function_queue(true);
-	if (local_softirq_pending())
-		do_softirq();
+
+	if (local_softirq_pending()) {
+
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+			do_softirq();
+		} else {
+			struct task_struct *ksoftirqd = this_cpu_ksoftirqd();
+
+			if (ksoftirqd && ksoftirqd->state != TASK_RUNNING)
+				wake_up_process(ksoftirqd);
+		}
+	}

 	local_irq_restore(flags);
 }