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

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Message-ID: <CAMRc=Md39C_7R39c5N9-ZUEZcT5bnE=uwx3gL=CNxPnxyytUUQ@mail.gmail.com>
Date:   Fri, 9 Nov 2018 12:09:06 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irq/irq_sim: add locking

pt., 9 lis 2018 o 11:19 Thomas Gleixner <tglx@...utronix.de> napisał(a):
>
> On Thu, 8 Nov 2018, Uwe Kleine-König wrote:
> > On Thu, Nov 08, 2018 at 05:47:48PM +0100, Bartosz Golaszewski wrote:
> > > @@ -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.
>
> Right. So the obvious solution is to avoid the irq number store and use a
> bitfield instead.
>
> struct irq_sim_work_ctx {
>        ...
>        unsigned long    pending;
> };
>
> fire(sim, offset)
> {
>         if (!sim->irqs[offset].enabled)
>                 return;
>
>         set_bit(offset, &sim->work_ctx.pending);
>         ....
>
> and in the work handler do:
>
> handle(work)
> {
>         struct irq_sim_work_ctx *ctx = container_of(work,....);
>
>         while (ctx->pending) {
>                 offs = ffs(ctx->pending);
>                 clr_bit(offs, &ctx->pending);
>                 handle_simple_irq(offs);
>         }
> }
>
> Or something like that.
>
> Thanks,
>
>         tglx

Actually on ARM and x86 with smp the handler is called between the
mutex lock and unlock alright but this solution looks much better.
I'll resend a v2.

Thanks!
Bartosz