linux-kernel - Re: [PATCH 05/10] mm, oom: skip vforked tasks from being selected

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Message-ID: <20160615145106.GC7944@redhat.com>
Date:	Wed, 15 Jun 2016 16:51:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	linux-mm@...ck.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 05/10] mm, oom: skip vforked tasks from being selected

On 06/09, Michal Hocko wrote:
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1883,6 +1883,32 @@ extern int arch_task_struct_size __read_mostly;
>  #define TNF_FAULT_LOCAL	0x08
>  #define TNF_MIGRATE_FAIL 0x10
>  
> +static inline bool in_vfork(struct task_struct *tsk)
> +{
> +	bool ret;
> +
> +	/*
> +	 * need RCU to access ->real_parent if CLONE_VM was used along with
> +	 * CLONE_PARENT.
> +	 *
> +	 * We check real_parent->mm == tsk->mm because CLONE_VFORK does not
> +	 * imply CLONE_VM
> +	 *
> +	 * CLONE_VFORK can be used with CLONE_PARENT/CLONE_THREAD and thus
> +	 * ->real_parent is not necessarily the task doing vfork(), so in
> +	 * theory we can't rely on task_lock() if we want to dereference it.
> +	 *
> +	 * And in this case we can't trust the real_parent->mm == tsk->mm
> +	 * check, it can be false negative. But we do not care, if init or
> +	 * another oom-unkillable task does this it should blame itself.
> +	 */
> +	rcu_read_lock();
> +	ret = tsk->vfork_done && tsk->real_parent->mm == tsk->mm;
> +	rcu_read_unlock();
> +
> +	return ret;
> +}

ACK, but why sched.h ? It has a single caller in oom_kill.c.

Oleg.