linux-kernel - Re: [PATCH] irq/irq

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Date:   Thu, 8 Nov 2018 20:41:16 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irq/irq_sim: add locking

Hello Bartosz,

On Thu, Nov 08, 2018 at 05:47:48PM +0100, Bartosz Golaszewski wrote:
> Two threads can try to fire the irq_sim with different offsets and will
> end up fighting for the irq_work asignment. To fix it: add a mutex and
> lock it before firing.
> 
> Suggested-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
> ---
>  include/linux/irq_sim.h | 1 +
>  kernel/irq/irq_sim.c    | 5 +++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/include/linux/irq_sim.h b/include/linux/irq_sim.h
> index 630a57e55db6..676bfa0c12b9 100644
> --- a/include/linux/irq_sim.h
> +++ b/include/linux/irq_sim.h
> @@ -29,6 +29,7 @@ struct irq_sim {
>  	int			irq_base;
>  	unsigned int		irq_count;
>  	struct irq_sim_irq_ctx	*irqs;
> +	struct mutex		lock;
>  };
>  
>  int irq_sim_init(struct irq_sim *sim, unsigned int num_irqs);
> diff --git a/kernel/irq/irq_sim.c b/kernel/irq/irq_sim.c
> index dd20d0d528d4..2f06c24b51a0 100644
> --- a/kernel/irq/irq_sim.c
> +++ b/kernel/irq/irq_sim.c
> @@ -74,6 +74,7 @@ int irq_sim_init(struct irq_sim *sim, unsigned int num_irqs)
>  	}
>  
>  	init_irq_work(&sim->work_ctx.work, irq_sim_handle_irq);
> +	mutex_init(&sim->lock);
>  	sim->irq_count = num_irqs;
>  
>  	return sim->irq_base;
> @@ -142,10 +143,14 @@ EXPORT_SYMBOL_GPL(devm_irq_sim_init);
>   */
>  void irq_sim_fire(struct irq_sim *sim, unsigned int offset)
>  {
> +	mutex_lock(&sim->lock);
> +
>  	if (sim->irqs[offset].enabled) {
>  		sim->work_ctx.irq = irq_sim_irqnum(sim, offset);
>  		irq_work_queue(&sim->work_ctx.work);
>  	}
> +
> +	mutex_unlock(&sim->lock);

This doesn't fix the issue I think. irq_work_queue() only schedules the
work function. If after irq_sim_fire() returned but before the worker
runs another irq_sim_fire() is issued the value is still overwritten.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |