Re:Re: [PATCH] sched: fix BUG in preempt_notifier

[cfme_admin]

This is a better way to solve this bug.
Thanks. 

At 2015-07-01 15:41:28, "Wanpeng Li" <wanpeng.li@xxxxxxxxxxx> wrote:
>
>
>On 7/1/15 2:33 PM, Lidong Chen wrote:
>> Signed-off-by: Lidong Chen <cfme_admin@xxxxxxx>
>
>Subject: sched,kvm: Fix KVM preempt_notifier usage
>
>The preempt-notifier API needs to sleep with the addition of the
>static_key, we do however need to hold off preemption while modifying
>the preempt notifier list, otherwise a preemption could observe an
>inconsistent list state.
>
>There is no reason to have preemption disabled in the caller,
>registering a preempt notifier is a purely task local affair.
>
>Therefore move the preempt_disable into the functions and change the
>callers to a preemptible context.
>
>Cc: Gleb Natapov<gleb@xxxxxxxxxx>
>Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
>Reported-and-Tested-by: Pontus Fuchs<pontus.fuchs@xxxxxxxxx>
>Signed-off-by: Peter Zijlstra (Intel)<peterz@xxxxxxxxxxxxx>
>
>
>If this commit in tip tree fix your bug?
>
>Regards,
>Wanpeng Li
>
>> ---
>>   kernel/sched/core.c | 25 ++++---------------------
>>   1 file changed, 4 insertions(+), 21 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index b803e1b..4a5a964 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2318,15 +2318,12 @@ void wake_up_new_task(struct task_struct *p)
>>   
>>   #ifdef CONFIG_PREEMPT_NOTIFIERS
>>   
>> -static struct static_key preempt_notifier_key = STATIC_KEY_INIT_FALSE;
>> -
>>   /**
>>    * preempt_notifier_register - tell me when current is being preempted & rescheduled
>>    * @notifier: notifier struct to register
>>    */
>>   void preempt_notifier_register(struct preempt_notifier *notifier)
>>   {
>> -	static_key_slow_inc(&preempt_notifier_key);
>>   	hlist_add_head(&notifier->link, &current->preempt_notifiers);
>>   }
>>   EXPORT_SYMBOL_GPL(preempt_notifier_register);
>> @@ -2340,11 +2337,10 @@ EXPORT_SYMBOL_GPL(preempt_notifier_register);
>>   void preempt_notifier_unregister(struct preempt_notifier *notifier)
>>   {
>>   	hlist_del(&notifier->link);
>> -	static_key_slow_dec(&preempt_notifier_key);
>>   }
>>   EXPORT_SYMBOL_GPL(preempt_notifier_unregister);
>>   
>> -static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)
>> +static void fire_sched_in_preempt_notifiers(struct task_struct *curr)
>>   {
>>   	struct preempt_notifier *notifier;
>>   
>> @@ -2352,14 +2348,9 @@ static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)
>>   		notifier->ops->sched_in(notifier, raw_smp_processor_id());
>>   }
>>   
>> -static __always_inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
>> -{
>> -	if (static_key_false(&preempt_notifier_key))
>> -		__fire_sched_in_preempt_notifiers(curr);
>> -}
>>   
>>   static void
>> -__fire_sched_out_preempt_notifiers(struct task_struct *curr,
>> +fire_sched_out_preempt_notifiers(struct task_struct *curr,
>>   				   struct task_struct *next)
>>   {
>>   	struct preempt_notifier *notifier;
>> @@ -2368,21 +2359,13 @@ __fire_sched_out_preempt_notifiers(struct task_struct *curr,
>>   		notifier->ops->sched_out(notifier, next);
>>   }
>>   
>> -static __always_inline void
>> -fire_sched_out_preempt_notifiers(struct task_struct *curr,
>> -				 struct task_struct *next)
>> -{
>> -	if (static_key_false(&preempt_notifier_key))
>> -		__fire_sched_out_preempt_notifiers(curr, next);
>> -}
>> -
>>   #else /* !CONFIG_PREEMPT_NOTIFIERS */
>>   
>> -static inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
>> +static void fire_sched_in_preempt_notifiers(struct task_struct *curr)
>>   {
>>   }
>>   
>> -static inline void
>> +static void
>>   fire_sched_out_preempt_notifiers(struct task_struct *curr,
>>   				 struct task_struct *next)
>>   {
>