linux-kernel - Re: [PATCH 08/18] mm, fork: make dup_mmap wait for mmap

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Date:	Mon, 29 Feb 2016 18:54:18 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Alex Deucher <alexander.deucher@....com>,
	Alex Thorlton <athorlton@....com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Christian König <christian.koenig@....com>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	Davidlohr Bueso <dave@...olabs.net>,
	David Rientjes <rientjes@...gle.com>,
	"H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	linux-arch@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Petr Cermak <petrcermak@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 08/18] mm, fork: make dup_mmap wait for mmap_sem for
 write killable

On 02/29, Michal Hocko wrote:
>
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -413,7 +413,10 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
>  	unsigned long charge;
>  
>  	uprobe_start_dup_mmap();
> -	down_write(&oldmm->mmap_sem);
> +	if (down_write_killable(&oldmm->mmap_sem)) {
> +		uprobe_end_dup_mmap();
> +		return -EINTR;
> +	}

This is really cosmetic and subjective, I won't insist if you prefer it this way.

But perhaps it makes sense to add another "fail" label above uprobe_end_dup_mmap()
we already have... IMO it is always better to avoid duplicating when it comes to
"unlock".

Oleg.