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Message-ID: <87leg1z5c3.ffs@tglx>
Date: Fri, 30 Jun 2023 11:07:08 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc: linux-kernel@...r.kernel.org, kernel@...s.com,
Vincent Whitchurch <vincent.whitchurch@...s.com>
Subject: Re: [PATCH v2] genirq: Fix nested thread vs synchronize_hardirq()
deadlock
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.
Also this is open coding wake_threads_waitq().
> +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.
Thanks,
tglx
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