Re: [PATCH 1/1] mmap.c: find_vma: remove if(mm) check

From: Kautuk Consul
Date: Tue Mar 27 2012 - 23:43:01 EST

On Wed, Mar 28, 2012 at 3:42 AM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 26 Mar 2012 19:49:27 -0400
> Kautuk Consul <consul.kautuk@xxxxxxxxx> 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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