* Peter Zijlstra | 2013-11-21 11:19:13 [+0100]:
>On Wed, Nov 20, 2013 at 01:33:33AM +0100, Nicholas Mc Guire wrote:
>> From a7259c360b6c8b873f5fcf6d5eed0ae78534a6c5 Mon Sep 17 00:00:00 2001
>> From: Nicholas Mc Guire <der.herr@xxxxxxx>
>> Date: Wed, 20 Nov 2013 07:22:09 +0800
>> Subject: [PATCH] allow preemption in recursive migrate_disable call
>>
>> Minor cleanup in migrate_disable/migrate_enable. The recursive case
>> does not need to disable preemption as it is "pinned" to the current
>> cpu any way so it is safe to preempt it.
>>
>> No functional change to migrate_disable/enable
>>
>> Signed-off-by: Nicholas Mc Guire <der.herr@xxxxxxx>
>> ---
>> kernel/sched/core.c | 6 ++----
>> 1 files changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index a7fafc28..22fa2e2 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2418,13 +2418,12 @@ void migrate_disable(void)
>> }
>> #endif
>>
>> - preempt_disable();
>> if (p->migrate_disable) {
>> p->migrate_disable++;
>> - preempt_enable();
>> return;
>> }
>>
>> + preempt_disable();
>> preempt_lazy_disable();
>> pin_current_cpu();
>> p->migrate_disable = 1;
>> @@ -2454,13 +2453,12 @@ void migrate_enable(void)
>> #endif
>> WARN_ON_ONCE(p->migrate_disable <= 0);
>>
>> - preempt_disable();
>> if (migrate_disable_count(p) > 1) {
>> p->migrate_disable--;
>> - preempt_enable();
>> return;
>> }
>>
>> + preempt_disable();
>> if (unlikely(migrate_disabled_updated(p))) {
>> /*
>> * Undo whatever update_migrate_disable() did, also see there
>
>Is there a reason one uses p->migrate_disable and the other uses
>migrate_disable_count(p) ?
After staring at code I would say migrate_disable() needs to ignore
MIGRATE_DISABLE_SET_AFFIN in order to complete. In the migrate_disable()
case it simply doesn't matter if it is set and it can't be set for the 0
case.
I was a little worried because the preempt_disable() also protects
counter during add/substract operations but since there can only be one
task at a time doing this, there should be no problem.
>Other than that,
>
>Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Sebastian
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