[tip: irq/core] genirq: Warn about using IRQF_ONESHOT without a threaded handler

["tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@linutronix.de>]

The following commit has been merged into the irq/core branch of tip:

Commit-ID:     aef30c8d569c0f31715447525640044c74feb26f
Gitweb:        https://git.kernel.org/tip/aef30c8d569c0f31715447525640044c74feb26f
Author:        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate:    Mon, 12 Jan 2026 14:40:13 +01:00
Committer:     Thomas Gleixner <tglx@kernel.org>
CommitterDate: Tue, 13 Jan 2026 09:56:25 +01:00

genirq: Warn about using IRQF_ONESHOT without a threaded handler

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
---
 kernel/irq/manage.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index bc2d36b..dde1aa6 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1474,6 +1474,13 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 		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.
 	 */