linux-kernel - Re: [PATCH] mm: mmap: Check all failures before set values

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Message-ID: <20150824135716.GO17078@dhcp22.suse.cz>
Date:	Mon, 24 Aug 2015 15:57:16 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Chen Gang <xili_gchen_5257@...mail.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"riel@...hat.com" <riel@...hat.com>,
	"sasha.levin@...cle.com" <sasha.levin@...cle.com>,
	"gang.chen.5i5j@...il.com" <gang.chen.5i5j@...il.com>,
	Linux Memory <linux-mm@...ck.org>,
	kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: mmap: Check all failures before set values

On Mon 24-08-15 21:34:25, Chen Gang wrote:
> On 8/24/15 19:32, Michal Hocko wrote:
> > On Mon 24-08-15 00:59:39, gang.chen.5i5j@...com wrote:
> >>> From: Chen Gang <gang.chen.5i5j@...il.com>
> >>>
> >>> When failure occurs and return, vma->vm_pgoff is already set, which is
> >>> not a good idea.
> > Why? The vma is not inserted anywhere and the failure path is supposed
> > to simply free the vma.
> >
> 
> It can save several insns when failure occurs.

The failure is quite unlikely, though.

> It is always a little better to let the external function suppose fewer
> callers' behalf.

I am sorry but I do not understand what you are saying here.

> It can save the code readers' (especially new readers') time resource
> to avoid to analyze why set 'vma->vm_pgoff' before checking '-ENOMEM'
> (may it cause issue? or is 'vm_pgoff' related with the next checking?).

Then your changelog should be specific about these reasons. "not a good
idea" is definitely not a good justification for a patch. I am not
saying the patch is incorrect I just do not sure it is worth it. The
code is marginally better. But others might think otherwise. The
changelog needs some more work for sure.
-- 
Michal Hocko
SUSE Labs
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