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SubjectRe: [PATCH] irq/irq_sim: add locking
czw., 8 lis 2018 o 20:41 Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> napisał(a):
>
> 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.
>

Looking at irq_work_queue(): while there may be some arch-specific
details deeper down the stack, it seems that unless the work is
IRQ_WORK_LAZY, the handler should be executed immediately. I'll verify
tomorrow though.

Bart

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