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genirq: Warn about using IRQF_ONESHOT without a threaded handler

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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@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patch.msgid.link/20260112134013.eQWyReHR@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2026-01-12 14:40:13 +01:00 • committed by Thomas Gleixner
parent 90876d9b37
commit aef30c8d56
1 changed files with 7 additions and 0 deletions
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7
kernel/irq/manage.c
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@ -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.