Re: [PATCH 0/4] CPU hotplug, cpusets: Fix CPU online handling related to cpusets

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Thu, 2012-02-23 at 15:27 +0530, Srivatsa S. Bhat wrote:
> From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Subject: CPU hotplug, cpusets, suspend: Don't touch cpusets during suspend/resume
> 
> Currently, during CPU hotplug, the cpuset callbacks modify the cpusets
> to reflect the state of the system, and this handling is asymmetric.
> That is, upon CPU offline, that CPU is removed from all cpusets. However
> when it comes back online, it is put back only to the root cpuset.
> 
> This gives rise to a significant problem during suspend/resume. During
> suspend, we offline all non-boot cpus and during resume we online them back.
> Which means, after a resume, all cpusets (except the root cpuset) will be
> restricted to just one single CPU (the boot cpu). But the whole point of
> suspend/resume is to restore the system to a state which is as close as
> possible to how it was before suspend.
> 
> So to fix this, don't touch cpusets during suspend/resume. That is, modify
> the cpuset-related CPU hotplug callback to just ignore CPU hotplug when it
> is initiated as part of the suspend/resume sequence.
> 
> Reported-by: Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Cc: stable@vger.kernel.org

Fair enough, I'll take it and push it through sched/urgent so that it
should still make 3.4.

> ---
> 
>  kernel/sched/core.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1169246..49ba9d4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6728,7 +6728,7 @@ int __init sched_create_sysfs_power_savings_entries(struct device *dev)
>  static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
>                              void *hcpu)
>  {
> -       switch (action & ~CPU_TASKS_FROZEN) {
> +       switch (action) {
>         case CPU_ONLINE:
>         case CPU_DOWN_FAILED:
>                 cpuset_update_active_cpus();
> @@ -6741,7 +6741,7 @@ static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
>  static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
>                                void *hcpu)
>  {
> -       switch (action & ~CPU_TASKS_FROZEN) {
> +       switch (action) {
>         case CPU_DOWN_PREPARE:
>                 cpuset_update_active_cpus();
>                 return NOTIFY_OK;
> 
> 
>