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

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Message-Id: <20120327151238.302a5920.akpm@linux-foundation.org>
Date:	Tue, 27 Mar 2012 15:12:38 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kautuk Consul <consul.kautuk@...il.com>
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 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;

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.
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