[PATCH] alpha: Send stop IPI to send to online CPUs

[PATCH] alpha: Send stop IPI to send to online CPUs

[Prarit Bhargava]

Unfortunately I do not have any HW to test this patch.  Hopefully someone on
the cc list can help me out?

P.

---8<---

This issue was noticed while debugging a shutdown issue where some
secondary CPUs are not being shutdown correctly.  A fix for that [1] requires
that secondary cpus be offlined using the cpu_online_mask so that the
stop operation is a no-op if CPU HOTPLUG is disabled.  I, like the author in
[1] looked at the architectures and found that alpha is one of two
architectures that executes smp_send_stop() on all possible CPUs.

On alpha, smp_send_stop() sends an IPI to all possible CPUs but only needs
to send them to online CPUs.

Send the stop IPI to only the online CPUs.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>

[1] https://lkml.org/lkml/2020/1/10/250
---
 arch/alpha/kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
index f4dd9f3f3001..f3a58c1fdd55 100644
--- a/arch/alpha/kernel/smp.c
+++ b/arch/alpha/kernel/smp.c
@@ -583,7 +583,7 @@ void
 smp_send_stop(void)
 {
 	cpumask_t to_whom;
-	cpumask_copy(&to_whom, cpu_possible_mask);
+	cpumask_copy(&to_whom, cpu_online_mask);
 	cpumask_clear_cpu(smp_processor_id(), &to_whom);
 #ifdef DEBUG_IPI_MSG
 	if (hard_smp_processor_id() != boot_cpu_id)
-- 
2.29.2