[PATCH 2.6.20] tasks cannot run on cpus onlined after boot

[PATCH 2.6.20] tasks cannot run on cpus onlined after boot

[Nathan Lynch]

Commit 5c1e176781f43bc902a51e5832f789756bff911b ("sched: force
/sbin/init off isolated cpus") sets init's cpus_allowed to a subset of
cpu_online_map at boot time, which means that tasks won't be scheduled
on cpus that are added to the system later.

Make init's cpus_allowed a subset of cpu_possible_map instead.  This
should still preserve the behavior that Nick's change intended.

Thanks to Giuliano Pochini for reporting this and testing the fix:

http://ozlabs.org/pipermail/linuxppc-dev/2006-December/029397.html


Signed-off-by: Nathan Lynch <ntl@pobox.com>

---

This is a regression from 2.6.18.  Assuming this change is okay, this
should go to -stable for 2.6.19.x.

diff --git a/kernel/sched.c b/kernel/sched.c
index b515e3c..3c8b1c5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6875,7 +6875,7 @@ void __init sched_init_smp(void)
 
 	lock_cpu_hotplug();
 	arch_init_sched_domains(&cpu_online_map);
-	cpus_andnot(non_isolated_cpus, cpu_online_map, cpu_isolated_map);
+	cpus_andnot(non_isolated_cpus, cpu_possible_map, cpu_isolated_map);
 	if (cpus_empty(non_isolated_cpus))
 		cpu_set(smp_processor_id(), non_isolated_cpus);
 	unlock_cpu_hotplug();

Re: [PATCH 2.6.20] tasks cannot run on cpus onlined after boot

[Ingo Molnar]

* Nathan Lynch <ntl@pobox.com> wrote:

> Commit 5c1e176781f43bc902a51e5832f789756bff911b ("sched: force
> /sbin/init off isolated cpus") sets init's cpus_allowed to a subset of
> cpu_online_map at boot time, which means that tasks won't be scheduled
> on cpus that are added to the system later.
> 
> Make init's cpus_allowed a subset of cpu_possible_map instead.  This 
> should still preserve the behavior that Nick's change intended.
> 
> Thanks to Giuliano Pochini for reporting this and testing the fix:
> 
> http://ozlabs.org/pipermail/linuxppc-dev/2006-December/029397.html
> 
> Signed-off-by: Nathan Lynch <ntl@pobox.com>

nicely spotted!

> -	cpus_andnot(non_isolated_cpus, cpu_online_map, cpu_isolated_map);
> +	cpus_andnot(non_isolated_cpus, cpu_possible_map, cpu_isolated_map);

Acked-by: Ingo Molnar <mingo@elte.hu>

	Ingo