linux-kernel - Re: [PATCH v2] shm: add split function to shm_vm

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Date:   Wed, 21 Mar 2018 15:53:56 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] shm: add split function to shm_vm_ops

On 03/21/2018 01:56 PM, Andrew Morton wrote:
> On Wed, 21 Mar 2018 09:13:14 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:
>>  
>> +static int shm_split(struct vm_area_struct *vma, unsigned long addr)
>> +{
>> +	struct file *file = vma->vm_file;
>> +	struct shm_file_data *sfd = shm_file_data(file);
>> +
>> +	if (sfd->vm_ops && sfd->vm_ops->split)
>> +		return sfd->vm_ops->split(vma, addr);
> 
> This will be the only site which tests for NULL shm_file_data.vm_ops. 
> It's a can't-happen, methinks.

You are correct, thanks for catching this.

> 
> I think I'll leave it as it is for now and will queue up a non-urgent
> patch:
> 
> 
> 
> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: ipc/shm.c: shm_split(): remove unneeded test for NULL shm_file_data.vm_ops
> 
> This was added by the recent "ipc/shm.c: add split function to
> shm_vm_ops", but it is not necessary.
> 
> Cc: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Davidlohr Bueso <dave@...olabs.net>
> Cc: Manfred Spraul <manfred@...orfullife.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Looks good, FWIW
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

-- 
Mike Kravetz

> ---
> 
>  ipc/shm.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff -puN ipc/shm.c~ipc-shmc-shm_split-remove-unneeded-test-for-null-shm_file_datavm_ops ipc/shm.c
> --- a/ipc/shm.c~ipc-shmc-shm_split-remove-unneeded-test-for-null-shm_file_datavm_ops
> +++ a/ipc/shm.c
> @@ -391,7 +391,7 @@ static int shm_split(struct vm_area_stru
>  	struct file *file = vma->vm_file;
>  	struct shm_file_data *sfd = shm_file_data(file);
>  
> -	if (sfd->vm_ops && sfd->vm_ops->split)
> +	if (sfd->vm_ops->split)
>  		return sfd->vm_ops->split(vma, addr);
>  
>  	return 0;
> _
>