linux-kernel - Re: [PATCH 13/18] exec: make exec path waiting for mmap

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Date:	Mon, 29 Feb 2016 18:23:34 +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>,
	Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 13/18] exec: make exec path waiting for mmap_sem killable

On 02/29, Michal Hocko wrote:
>
> @@ -267,7 +267,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
>  	if (!vma)
>  		return -ENOMEM;
>  
> -	down_write(&mm->mmap_sem);
> +	if (down_write_killable(&mm->mmap_sem)) {
> +		err = -EINTR;
> +		goto err_free;
> +	}
>  	vma->vm_mm = mm;

I won't argue, but this looks unnecessary. Nobody else can see this new mm,
down_write() can't block.

In fact I think we can just remove down_write/up_write here. Except perhaps
there is lockdep_assert_held() somewhere in these paths.

Oleg.