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

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index bc2d36b6b13b0fdfb9f2d7b8e92ecf91dba76c25..dde1aa62ffe80d0d66a5b371b78d100f172160f7 100644 (file)
--- 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.