[PATCH] genirq: Take the proposed affinity at face value if force==true

[Marc Zyngier]

Although setting the affinity of an interrupt to a set of CPUs
that doesn't have any online CPU is generally frowned apon,
there are a few limited cases where such affinity is set from
a CPUHP notifier, setting the affinity to a CPU that isn't online
yet.

The saving grace is that this is always done using the 'force'
attribute, which gives us a hint that we really shouldn't worry
too much about the affinity at this stage, and that the caller
knows best. Or so we hope.

This restores the expected behaviour on Marek's system.

Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Link:: https://lore.kernel.org/r/4b7fc13c-887b-a664-26e8-45aed13f048a@xxxxxxxxxxx
---
 kernel/irq/manage.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index f71ecc100545..f1d5a94c6c9f 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -266,10 +266,16 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
 		prog_mask = mask;
 	}
 
-	/* Make sure we only provide online CPUs to the irqchip */
+	/*
+	 * Make sure we only provide online CPUs to the irqchip,
+	 * unless we are being asked to force the affinity (in which
+	 * case we do as we are told).
+	 */
 	cpumask_and(&tmp_mask, prog_mask, cpu_online_mask);
-	if (!cpumask_empty(&tmp_mask))
+	if (!force && !cpumask_empty(&tmp_mask))
 		ret = chip->irq_set_affinity(data, &tmp_mask, force);
+	else if (force)
+		ret = chip->irq_set_affinity(data, mask, force);
 	else
 		ret = -EINVAL;
 
-- 
2.34.1