linux-kernel - Re: [PATCH] IRQ, cpu-hotplug: Fix a race between CPU hotplug and IRQ desc alloc/free

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Date:   Mon, 4 Sep 2017 11:23:01 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Huang, Ying" <ying.huang@...el.com>
cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IRQ, cpu-hotplug: Fix a race between CPU hotplug and
 IRQ desc alloc/free

On Mon, 4 Sep 2017, Huang, Ying wrote:
> diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
> index 638eb9c83d9f..af9029625271 100644
> --- a/kernel/irq/cpuhotplug.c
ry> +++ b/kernel/irq/cpuhotplug.c
> @@ -129,10 +129,13 @@ void irq_migrate_all_off_this_cpu(void)
>  	struct irq_desc *desc;
>  	unsigned int irq;
>  
> +	irq_lock_sparse();

You cannot take that lock here as irq_migrate_all_off_this_cpu() is called
with interrupts disabled.

The protection in takedown_cpus() is wrong. Patch below.

Thanks,

	tglx
----

--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -642,13 +642,13 @@ static int takedown_cpu(unsigned int cpu
 	wait_for_completion(&st->done);
 	BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);
 
-	/* Interrupts are moved away from the dying cpu, reenable alloc/free */
-	irq_unlock_sparse();
-
 	hotplug_cpu__broadcast_tick_pull(cpu);
 	/* This actually kills the CPU. */
 	__cpu_die(cpu);
 
+	/* Interrupts are moved away from the dying cpu, reenable alloc/free */
+	irq_unlock_sparse();
+
 	tick_cleanup_dead_cpu(cpu);
 	return 0;
 }