From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 5/6] kmod: Add new call_usermodehelper_timeout() API
Date: Tue, 27 Mar 2012 17:43:05 +0200
Message-ID: <20120327154305.GA19314@redhat.com>
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Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Tetsuo Handa <penguin-kernel-JPay3/Yim36HaxMnTkn67Xf5DAMn2ifp@public.gmane.org>,
	linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>,
	Peter Zijlstra <a.p.zijlstra-/NLkJaSkS4VmR6Xm/wNWPw@public.gmane.org>,
	Paul Turner <pjt-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	linux-fsdevel <linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
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	Trond Myklebust <Trond.Myklebust-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>,
	"Bhamare, Sachin" <sbhamare-C4P08NqkoRlBDgjK7y7TUQ@public.gmane.org>,
	David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
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	Greg KH <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
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To: Boaz Harrosh <bharrosh-C4P08NqkoRlBDgjK7y7TUQ@public.gmane.org>
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Hi Boaz,

I'll read this series tomorrow, but

On 03/26, Boaz Harrosh wrote:
>
>  int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
>  {
>  	DECLARE_COMPLETION_ONSTACK(done);
> +	int wait_state;
>  	int retval = 0;
>
>  	helper_lock();
> @@ -540,19 +541,15 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
>  	if (wait == UMH_NO_WAIT)	/* task has freed sub_info */
>  		goto unlock;
>
> -	if (wait & UMH_KILLABLE) {
> -		retval = wait_for_completion_killable(&done);
> -		if (!retval)
> -			goto wait_done;
> -
> +	wait_state = (wait & UMH_KILLABLE) ? TASK_KILLABLE : 0;
> +	retval = wait_for_completion_timeout_state(&done, sub_info->timeout,
> +						   wait_state);
> +	if (unlikely(retval)) {
>  		/* umh_complete() will see NULL and free sub_info */
>  		if (xchg(&sub_info->complete, NULL))
>  			goto unlock;
> -		/* fallthrough, umh_complete() was already called */
>  	}
>
> -	wait_for_completion(&done);

at first glance this looks certainly wrong, or I misread the patch.

We can't remove the "fallback to wait_for_completion" logic until
you move the completion into subprocess_info (the next patch seems
to do this).

xchg() can race with umh_complete(). If it returns NULL, umh_complete()
was already called and got ->complete != NULL, we must not return until
umh_complete() finishes complete().

Oleg.

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