linux-kernel - Re: [PATCH] sched: fix BUG in preempt

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Date:	Wed, 1 Jul 2015 15:41:28 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Lidong Chen <cfme_admin@....com>, mingo@...hat.com,
	peterz@...radead.org
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: fix BUG in preempt_notifier



On 7/1/15 2:33 PM, Lidong Chen wrote:
> Signed-off-by: Lidong Chen <cfme_admin@....com>

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@...nel.org>
Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
Reported-and-Tested-by: Pontus Fuchs<pontus.fuchs@...il.com>
Signed-off-by: Peter Zijlstra (Intel)<peterz@...radead.org>


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)
>   {

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