linux-kernel - Re: [PATCH 1/2] taskstats: add_del_listener() shouldn't use the wrong node

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Date:	Thu, 21 Jul 2011 14:28:48 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Balbir Singh <bsingharora@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] taskstats: add_del_listener() shouldn't use the wrong
 node

On 07/20/2011 09:00 PM, Oleg Nesterov wrote:
> 1. 26c4caea "don't allow duplicate entries in listener mode"
>    changed add_del_listener(REGISTER) so that "next_cpu:" can
>    reuse the listener allocated for the previous cpu, this
>    doesn't look exactly right even if minor.

That construction is somewhat unusual. I agree that this code looks cleaner
and probably reduces the risk that someone in the future misunderstand the
code.

> 
>    Change the code to kfree() in the already-registered case,
>    this case is unlikely anyway so the extra kmalloc_node()
>    shouldn't hurt but looke more correct and clean.
> 
> 2. use the plain list_for_each_entry() instead of _safe() to
>    scan listeners->list.
> 
> 3. Remove the unneeded INIT_LIST_HEAD(&s->list), we are going
>    to list_add(&s->list).
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Jerome Marchand <jmarchan@...hat.com>

> ---
> 
>  kernel/taskstats.c |   16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> --- ts/kernel/taskstats.c~1_cleanup	2011-07-03 16:27:57.000000000 +0200
> +++ ts/kernel/taskstats.c	2011-07-20 19:35:38.000000000 +0200
> @@ -291,30 +291,28 @@ static int add_del_listener(pid_t pid, c
>  	if (!cpumask_subset(mask, cpu_possible_mask))
>  		return -EINVAL;
>  
> -	s = NULL;
>  	if (isadd == REGISTER) {
>  		for_each_cpu(cpu, mask) {
> -			if (!s)
> -				s = kmalloc_node(sizeof(struct listener),
> -						 GFP_KERNEL, cpu_to_node(cpu));
> +			s = kmalloc_node(sizeof(struct listener),
> +					GFP_KERNEL, cpu_to_node(cpu));
>  			if (!s)
>  				goto cleanup;
> +
>  			s->pid = pid;
> -			INIT_LIST_HEAD(&s->list);
>  			s->valid = 1;
>  
>  			listeners = &per_cpu(listener_array, cpu);
>  			down_write(&listeners->sem);
> -			list_for_each_entry_safe(s2, tmp, &listeners->list, list) {
> +			list_for_each_entry(s2, &listeners->list, list) {
>  				if (s2->pid == pid)
> -					goto next_cpu;
> +					goto exists;
>  			}
>  			list_add(&s->list, &listeners->list);
>  			s = NULL;
> -next_cpu:
> +exists:
>  			up_write(&listeners->sem);
> +			kfree(s); /* nop if NULL */
>  		}
> -		kfree(s);
>  		return 0;
>  	}
>  
> 

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