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SubjectRe: [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@pengutronix.de>
> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.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/ |

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