Re: [PATCH v2] shm: add split function to shm_vm_ops

[Mike Kravetz]

On 03/21/2018 01:56 PM, Andrew Morton wrote:
> On Wed, 21 Mar 2018 09:13:14 -0700 Mike Kravetz <mike.kravetz@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

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

-- 
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;
> _
>