Re: [PATCH] RDMA/siw: Fix user page pinning accounting

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Jan 30, 2023 at 02:28:04PM +0100, Bernard Metzler wrote:
> To avoid racing with other user memory reservations, immediately
> account full amount of pages to be pinned.
> 
> Fixes: 2251334dcac9 ("rdma/siw: application buffer management")
> Reported-by: Jason Gunthorpe <jgg@nvidia.com>
> Suggested-by: Alistair Popple <apopple@nvidia.com>
> Signed-off-by: Bernard Metzler <bmt@zurich.ibm.com>
> ---
>  drivers/infiniband/sw/siw/siw_mem.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
> index b2b33dd3b4fa..7cf4d927bbab 100644
> --- a/drivers/infiniband/sw/siw/siw_mem.c
> +++ b/drivers/infiniband/sw/siw/siw_mem.c
> @@ -398,7 +398,8 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
>  
>  	mlock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>  
> -	if (num_pages + atomic64_read(&mm_s->pinned_vm) > mlock_limit) {
> +	if (num_pages + atomic64_add_return(num_pages, &mm_s->pinned_vm) >
> +	    mlock_limit) {

???

Doesn't atomic_add_return return the result of adding num_pages and
pinned_vm? Then you add it again?

Jason