linux-kernel - Re: [RFC PATCH 5/9] sched: move task rq locking functions to sched.h

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Date:	Tue, 10 Feb 2015 19:48:17 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Seth Jennings <sjenning@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	Vojtech Pavlik <vojtech@...e.cz>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/9] sched: move task rq locking functions to sched.h

(2015/02/10 2:31), Josh Poimboeuf wrote:
> Move task_rq_lock/unlock() to sched.h so they can be used elsewhere.
> The livepatch code needs to lock each task's rq in order to safely
> examine its stack and switch it to a new patch universe.

Hmm, why don't you just expose (extern in sched.h) those?

Thank you,

> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  kernel/sched/core.c  | 32 --------------------------------
>  kernel/sched/sched.h | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+), 32 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b5797b7..78d91e6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -326,44 +326,12 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)
>  	}
>  }
>  
> -/*
> - * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
> - */
> -static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
> -	__acquires(p->pi_lock)
> -	__acquires(rq->lock)
> -{
> -	struct rq *rq;
> -
> -	for (;;) {
> -		raw_spin_lock_irqsave(&p->pi_lock, *flags);
> -		rq = task_rq(p);
> -		raw_spin_lock(&rq->lock);
> -		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
> -			return rq;
> -		raw_spin_unlock(&rq->lock);
> -		raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
> -
> -		while (unlikely(task_on_rq_migrating(p)))
> -			cpu_relax();
> -	}
> -}
> -
>  static void __task_rq_unlock(struct rq *rq)
>  	__releases(rq->lock)
>  {
>  	raw_spin_unlock(&rq->lock);
>  }
>  
> -static inline void
> -task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
> -	__releases(rq->lock)
> -	__releases(p->pi_lock)
> -{
> -	raw_spin_unlock(&rq->lock);
> -	raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
> -}
> -
>  /*
>   * this_rq_lock - lock this runqueue and disable interrupts.
>   */
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 9a2a45c..ae514c9 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1542,6 +1542,39 @@ static inline void double_rq_unlock(struct rq *rq1, struct rq *rq2)
>  
>  #endif
>  
> +/*
> + * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
> + */
> +static inline struct rq *task_rq_lock(struct task_struct *p,
> +				      unsigned long *flags)
> +	__acquires(p->pi_lock)
> +	__acquires(rq->lock)
> +{
> +	struct rq *rq;
> +
> +	for (;;) {
> +		raw_spin_lock_irqsave(&p->pi_lock, *flags);
> +		rq = task_rq(p);
> +		raw_spin_lock(&rq->lock);
> +		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
> +			return rq;
> +		raw_spin_unlock(&rq->lock);
> +		raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
> +
> +		while (unlikely(task_on_rq_migrating(p)))
> +			cpu_relax();
> +	}
> +}
> +
> +static inline void task_rq_unlock(struct rq *rq, struct task_struct *p,
> +				  unsigned long *flags)
> +	__releases(rq->lock)
> +	__releases(p->pi_lock)
> +{
> +	raw_spin_unlock(&rq->lock);
> +	raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
> +}
> +
>  extern struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq);
>  extern struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq);
>  extern void print_cfs_stats(struct seq_file *m, int cpu);
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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