linux-kernel - Re: [PATCH v3 1/2] irq: abstract irqaction handler invocation

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Message-ID: <20210715111531.GA56828@C02TD0UTHF1T.local>
Date:   Thu, 15 Jul 2021 12:15:31 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, maz@...nel.org,
        paulmck@...nel.org
Subject: Re: [PATCH v3 1/2] irq: abstract irqaction handler invocation

On Thu, Jul 15, 2021 at 12:49:54PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 15, 2021 at 10:50:30AM +0100, Mark Rutland wrote:
> > diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
> > index 54363527feea..70a4694cc891 100644
> > --- a/kernel/irq/internals.h
> > +++ b/kernel/irq/internals.h
> > @@ -11,6 +11,8 @@
> >  #include <linux/pm_runtime.h>
> >  #include <linux/sched/clock.h>
> >  
> > +#include <trace/events/irq.h>
> > +
> >  #ifdef CONFIG_SPARSE_IRQ
> >  # define IRQ_BITMAP_BITS	(NR_IRQS + 8196)
> >  #else
> > @@ -107,6 +109,32 @@ irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc, unsigned int *flags
> >  irqreturn_t handle_irq_event_percpu(struct irq_desc *desc);
> >  irqreturn_t handle_irq_event(struct irq_desc *desc);
> >  
> > +static inline irqreturn_t __handle_irqaction(unsigned int irq,
> > +					     struct irqaction *action,
> > +					     void *dev_id)
> > +{
> > +	irqreturn_t res;
> > +
> > +	trace_irq_handler_entry(irq, action);
> > +	res = action->handler(irq, dev_id);
> > +	trace_irq_handler_exit(irq, action, res);
> > +
> > +	return res;
> > +}
> > +
> > +static inline irqreturn_t handle_irqaction(unsigned int irq,
> > +					   struct irqaction *action)
> > +{
> > +	return __handle_irqaction(irq, action, action->dev_id);
> > +}
> > +
> > +static inline irqreturn_t handle_irqaction_percpu_devid(unsigned int irq,
> > +							struct irqaction *action)
> > +{
> > +	return __handle_irqaction(irq, action,
> > +				  raw_cpu_ptr(action->percpu_dev_id));
> > +}
> 
> So I like this patch, it's a nice cleanup.
> 
> However, you could implement the next patch as a module that hooks into
> those two tracepoints. Quite possibly the existing IRQ latency tracer
> would already work for what you need and also provide you a function
> trace of WTH the CPU was doing.

The issue with the existing tracers is that they're logging for
later/concurrent analysis, whereas what I need is a notification (e.g. a
WARN) when the maximum expected latency has been breached. That way it
gets caught by Syzkaller or whatever without needing to specially manage
the tracer.

If there's a way to do that (e.g. with boot-time options), I'm happy to
use that instead; I just couldn't see hwo to do that today, and was
under the impression that the existing tracepoints don't give quite what
I need (e.g. since the entry/exit hooks are separate, so I'd have to
store some state somewhere else).

I'm happy to take another look if you think I'm wrong on that. :)

Thanks,
Mark.