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Message-ID: <e52e4b71611c984281352d2fb1ab746ff09f4d10.camel@axis.com>
Date: Mon, 3 Jul 2023 09:28:52 +0000
From: Vincent Whitchurch <Vincent.Whitchurch@...s.com>
To: "tglx@...utronix.de" <tglx@...utronix.de>,
Vincent Whitchurch <Vincent.Whitchurch@...s.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
kernel <kernel@...s.com>
Subject: Re: [PATCH v2] genirq: Fix nested thread vs synchronize_hardirq()
deadlock
On Fri, 2023-06-30 at 11:07 +0200, Thomas Gleixner wrote:
> On Tue, Jun 20 2023 at 13:16, Vincent Whitchurch wrote:
> > --- a/kernel/irq/chip.c
> > +++ b/kernel/irq/chip.c
> > @@ -476,7 +476,7 @@ void handle_nested_irq(unsigned int irq)
> > }
> >
> >
> > kstat_incr_irqs_this_cpu(desc);
> > - irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);
> > + atomic_inc(&desc->threads_active);
> > raw_spin_unlock_irq(&desc->lock);
> >
> >
> > action_ret = IRQ_NONE;
> > @@ -487,7 +487,8 @@ void handle_nested_irq(unsigned int irq)
> > note_interrupt(desc, action_ret);
> >
> >
> > raw_spin_lock_irq(&desc->lock);
> > - irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);
> > + if (atomic_dec_and_test(&desc->threads_active))
> > + wake_up(&desc->wait_for_threads);
>
> This breaks on RT. The wakeup cannot be inside the raw spin-locked
> region.
OK. I will remove the acquisition of the spin lock at the end of this
function since it was only used for protecting the irqd flags.
> Also this is open coding wake_threads_waitq().
OK, that's in manage.c so I'll make it non-static and add it to
internals.h and use it from here.
> > +static void __synchronize_irq(struct irq_desc *desc)
> > +{
> > + __synchronize_hardirq(desc, true);
> > + /*
> > + * We made sure that no hardirq handler is
> > + * running. Now verify that no threaded handlers are
> > + * active.
> > + */
> > + wait_event(desc->wait_for_threads,
> > + !atomic_read(&desc->threads_active));
>
> Splitting this out is fine. Not reformatting it not so much.
Will fix.
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