linux-kernel - Re: [PATCH] oom killer: break from infinite loop

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Message-Id: <20100326150805.f5853d1c.akpm@linux-foundation.org>
Date:	Fri, 26 Mar 2010 15:08:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Anfei Zhou <anfei.zhou@...il.com>
Cc:	rientjes@...gle.com, kosaki.motohiro@...fujitsu.com,
	nishimura@....nes.nec.co.jp, kamezawa.hiroyu@...fujitsu.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] oom killer: break from infinite loop

On Thu, 25 Mar 2010 00:25:05 +0800
Anfei Zhou <anfei.zhou@...il.com> wrote:

> In multi-threading environment, if the current task(A) have got
> the mm->mmap_sem semaphore, and the thread(B) in the same process
> is selected to be oom killed, because they shares the same semaphore,
> thread B can not really be killed.  So __alloc_pages_slowpath turns
> to be a infinite loop.  Here set all the threads in the group to
> TIF_MEMDIE, it gets a chance to break and exit.
> 
> Signed-off-by: Anfei Zhou <anfei.zhou@...il.com>
> ---
>  mm/oom_kill.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 9b223af..aab9892 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -381,6 +381,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
>   */
>  static void __oom_kill_task(struct task_struct *p, int verbose)
>  {
> +	struct task_struct *t;
> +
>  	if (is_global_init(p)) {
>  		WARN_ON(1);
>  		printk(KERN_WARNING "tried to kill init!\n");
> @@ -412,6 +414,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>  	 */
>  	p->rt.time_slice = HZ;
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
> +	for (t = next_thread(p); t != p; t = next_thread(t))
> +		set_tsk_thread_flag(t, TIF_MEMDIE);
>  
>  	force_sig(SIGKILL, p);

Don't we need some sort of locking while walking that ring? 
Unintuitively it appears to be spin_lock_irq(&p->sighand->siglock).


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