Re: [PATCH] genirq: Warn about using IRQF_ONESHOT without a threaded handler

[Laurent Pinchart]

Hi Sebastian,

Thank you for the patch.

On Mon, Jan 12, 2026 at 02:40:13PM +0100, Sebastian Andrzej Siewior wrote:
> IRQF_ONESHOT disables the interrupt source until after the threaded
> handler completed its work. This is needed to allow the threaded handler
> to run - otherwise the CPU will get back to the interrupt handler
> because the interrupt source remains active and the threaded handler
> will not able to do its work.
> 
> Specifying IRQF_ONESHOT without a threaded handler does not make sense.
> It could be a leftover if the handler _was_ threaded and changed back to
> primary and the flag was not removed. This can be problematic in the
> `threadirqs' case because the handler is exempt from forced-threading.
> This in turn can become a problem on a PREEMPT_RT system if the handler
> attempts to acquire sleeping locks.
> 
> Warn about missing threaded handlers with the IRQF_ONESHOT flag.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> 
> This popped up after Stefan Klug posted
>    https://lore.kernel.org/all/20260105-sklug-v6-16-topic-dw100-v3-1-dev-v1-3-65af34d04fd8@xxxxxxxxxxxxxxxx/

This patch would have saved us from trouble with the DW100 driver, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>

I wonder if some people would object due to panic_on_warn, but I think
the issue will be caught early when testing kernel updates way before it
should hit users.

> There are a few drivers in tree which will trigger this warning such as
> - arch/arm/mach-versatile/spc.c
> - drivers/char/tpm/tpm_tis_spi_cr50.c
> - drivers/edac/altera_edac.c
> - drivers/i2c/busses/i2c-k1.c
> - …
> 
> just to name a few. I *think* if IRQF_ONESHOT was on purpose and not
> driven by copy/paste then the they wanted to use IRQF_NO_THREAD.
> 
>  kernel/irq/manage.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 349ae7979da0e..18a8405cadb26 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -1473,6 +1473,13 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
>  	if (!(new->flags & IRQF_TRIGGER_MASK))
>  		new->flags |= irqd_get_trigger_type(&desc->irq_data);
>  
> +	/*
> +	 * IRQF_ONESHOT means the interrupt source in the IRQ chip will be
> +	 * masked until the threaded handled is done. If there is no thread
> +	 * handler then it makes no sense to have IRQF_ONESHOT.
> +	 */
> +	WARN_ON_ONCE(new->flags & IRQF_ONESHOT && !new->thread_fn);
> +
>  	/*
>  	 * Check whether the interrupt nests into another interrupt
>  	 * thread.

-- 
Regards,

Laurent Pinchart