linux-kernel - Re: [PATCH 1/1] mmap.c: find

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Date:	Wed, 28 Mar 2012 09:13:00 +0530
From:	Kautuk Consul <consul.kautuk@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hugh Dickins <hughd@...gle.com>, Al Viro <viro@...iv.linux.org.uk>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mmap.c: find_vma: remove if(mm) check

On Wed, Mar 28, 2012 at 3:42 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 26 Mar 2012 19:49:27 -0400
> Kautuk Consul <consul.kautuk@...il.com> wrote:
>
>> find_vma is called from kernel code where it is absolutely
>> sure that the mm_struct arg being passed to it is non-NULL.
>>
>> Remove the if(mm) check.
>
> It's odd that the if(mm) test exists - I wonder why it was originally
> added.  My repo only goes back ten years, and it's there in 2.4.18.
>
> Any code which calls find_vma() without an mm is surely pretty busted?
>
>
> Still, I think I'd prefer to do
>
>        if (WARN_ON_ONCE(!mm))
>                return NULL;
>

yes, I agree. that is safe for now as there are a huge number of calls
to this API.

> then let that bake for a kernel release, just to find out if we have a
> weird caller out there, such as a function which is called by both user
> threads and by kernel threads.

ok. I'll spin another one and send it to you with your suggestions in a day or
two when I go back home after my day job.
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