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Subject: Re: [PATCH 3/8] vfork: make it killable
From: Matt Fleming <matt.fleming@linux.intel.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Roland McGrath <roland@hack.frob.com>, Tejun Heo <tj@kernel.org>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org
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	 <20110727163254.GC23793@redhat.com>
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Date: Fri, 29 Jul 2011 14:02:10 +0100
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On Wed, 2011-07-27 at 18:32 +0200, Oleg Nesterov wrote:

[...]
 
>  static long clone_vfork_finish(struct task_struct *child,
>  				struct completion *vfork_done, long pid)
>  {
> -	freezer_do_not_count();
> -	wait_for_completion(vfork_done);
> -	freezer_count();
> +	int killed = wait_for_completion_killable(vfork_done);
> +
> +	if (killed) {
> +		struct completion *steal = xchg(&child->vfork_done, NULL);
> +		/* if we race with complete_vfork_done() we have to wait */
> +		if (unlikely(!steal))
> +			wait_for_completion(vfork_done);
> +
> +		return -EINTR;
> +	}

Hmm.. isn't this inherently racy anyway? Why go to the trouble of trying
to handle this race at all?