linux-kernel - Re: [PATCH 5/5] oom: dump_tasks() use find_lock_task

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Message-ID: <20100602150304.GA5326@barrios-desktop>
Date:	Thu, 3 Jun 2010 00:03:04 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Oleg Nesterov <oleg@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 5/5] oom: dump_tasks() use find_lock_task_mm() too

Hi, Kosaki. 

On Tue, Jun 01, 2010 at 02:51:49PM +0900, KOSAKI Motohiro wrote:
> dump_task() should have the same process iteration logic as
> select_bad_process().
> 
> It is needed for protecting from task exiting race.
> 
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
>  mm/oom_kill.c |   31 +++++++++++++------------------
>  1 files changed, 13 insertions(+), 18 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index cbad4d4..a8af9e8 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -344,35 +344,30 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
>   */
>  static void dump_tasks(const struct mem_cgroup *mem)
>  {
> -	struct task_struct *g, *p;
> +	struct task_struct *p;
> +	struct task_struct *task;
>  
>  	printk(KERN_INFO "[ pid ]   uid  tgid total_vm      rss cpu oom_adj "
>  	       "name\n");
> -	do_each_thread(g, p) {
> +
> +	for_each_process(p) {
>  		struct mm_struct *mm;
>  
> -		if (mem && !task_in_mem_cgroup(p, mem))
> +		if (is_global_init(p) || (p->flags & PF_KTHREAD))

select_bad_process needs is_global_init check to not select init as victim.
But in this case, it is just for dumping information of tasks. 

>  			continue;
> -		if (!thread_group_leader(p))
> +		if (mem && !task_in_mem_cgroup(p, mem))
>  			continue;
>  
> -		task_lock(p);
> -		mm = p->mm;
> -		if (!mm) {
> -			/*
> -			 * total_vm and rss sizes do not exist for tasks with no
> -			 * mm so there's no need to report them; they can't be
> -			 * oom killed anyway.
> -			 */

Please, do not remove the comment for mm newbies unless you think it's useless.

> -			task_unlock(p);
> +		task = find_lock_task_mm(p);
> +		if (!task)
>  			continue;
> -		}
> +
>  		printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
> -		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
> -		       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
> +		       task->pid, __task_cred(task)->uid, task->tgid, task->mm->total_vm,
> +		       get_mm_rss(task->mm), (int)task_cpu(task), task->signal->oom_adj,
>  		       p->comm);
> -		task_unlock(p);
> -	} while_each_thread(g, p);
> +		task_unlock(task);
> +	}
>  }
>  
>  static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> -- 
> 1.6.5.2
> 
> 
> 
> --
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-- 
Kind regards,
Minchan Kim
--
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