linux-kernel - Re: [PATCH 1/2] hung_task: split for_each_process_thread() into for_each_process() + __for_each

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Date:	Fri, 20 Mar 2015 16:55:10 +0000
From:	Aaron Tomlin <atomlin@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	akpm@...ux-foundation.org, rientjes@...gle.com,
	dwysocha@...hat.com, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/2] hung_task: split for_each_process_thread() into
 for_each_process() + __for_each_thread()

On Tue 2015-03-17 20:25 +0100, Oleg Nesterov wrote:
> Preparation. Change the main loop in check_hung_uninterruptible_tasks()
> to use the nested for_each_process() + __for_each_thread() loops explicitly.
> Note that we use __for_each_thread(), not for_each_thread(). This way it
> is clear that the inner loop doesn't depend on 'g' after we read ->signal.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/hung_task.c |   23 ++++++++++++++---------
>  1 files changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index e0f90c2..4735b99 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -169,17 +169,22 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
>  		return;
>  
>  	rcu_read_lock();
> -	for_each_process_thread(g, t) {
> -		if (!max_count--)
> -			goto unlock;
> -		if (!--batch_count) {
> -			batch_count = HUNG_TASK_BATCHING;
> -			if (!rcu_lock_break(g, t))
> +	for_each_process(g) {
> +		struct signal_struct *sig = g->signal;
> +
> +		__for_each_thread(sig, t) {
> +			if (!max_count--)
>  				goto unlock;
> +
> +			if (!--batch_count) {
> +				batch_count = HUNG_TASK_BATCHING;
> +				if (!rcu_lock_break(g, t))
> +					goto unlock;
> +			}
> +			/* use "==" to skip the TASK_KILLABLE tasks */
> +			if (t->state == TASK_UNINTERRUPTIBLE)
> +				check_hung_task(t, timeout);
>  		}
> -		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
> -		if (t->state == TASK_UNINTERRUPTIBLE)
> -			check_hung_task(t, timeout);
>  	}
>   unlock:
>  	rcu_read_unlock();
> 

Acked-by: Aaron Tomlin <atomlin@...hat.com>
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