Re: [PATCH 1/1] IB/umem: use get_user_pages_fast() to pin DMA pages

[Ira Weiny]

On Fri, Nov 08, 2019 at 06:04:34PM -0800, John Hubbard wrote:
> And get rid of the mmap_sem calls, as part of that. Note
> that get_user_pages_fast() will, if necessary, fall back to
> __gup_longterm_unlocked(), which takes the mmap_sem as needed.
> 
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>

Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>

> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
>  drivers/infiniband/core/umem.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index 24244a2f68cc..3d664a2539eb 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -271,16 +271,13 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
>  	sg = umem->sg_head.sgl;
>  
>  	while (npages) {
> -		down_read(&mm->mmap_sem);
> -		ret = get_user_pages(cur_base,
> -				     min_t(unsigned long, npages,
> -					   PAGE_SIZE / sizeof (struct page *)),
> -				     gup_flags | FOLL_LONGTERM,
> -				     page_list, NULL);
> -		if (ret < 0) {
> -			up_read(&mm->mmap_sem);
> +		ret = get_user_pages_fast(cur_base,
> +					  min_t(unsigned long, npages,
> +						PAGE_SIZE /
> +						sizeof(struct page *)),
> +					  gup_flags | FOLL_LONGTERM, page_list);
> +		if (ret < 0)
>  			goto umem_release;
> -		}
>  
>  		cur_base += ret * PAGE_SIZE;
>  		npages   -= ret;
> @@ -288,8 +285,6 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
>  		sg = ib_umem_add_sg_table(sg, page_list, ret,
>  			dma_get_max_seg_size(context->device->dma_device),
>  			&umem->sg_nents);
> -
> -		up_read(&mm->mmap_sem);
>  	}
>  
>  	sg_mark_end(sg);
> -- 
> 2.24.0
>