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

[Thomas Gleixner]

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;
 }