On Tue, Jun 29, 2021 at 06:01:12PM +0200, Jesper Dangaard Brouer wrote:
> On 29/06/2021 15.48, Chuck Lever wrote:
>
> > The call site in __page_pool_alloc_pages_slow() also seems to be
> > confused on this matter. It should be attended to by someone who
> > is familiar with that code.
>
> I don't think we need a fix for __page_pool_alloc_pages_slow(), as the array
> is guaranteed to be empty.
>
> But a fix would look like this:
>
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index c137ce308c27..1b04538a3da3 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -245,22 +245,23 @@ static struct page
> *__page_pool_alloc_pages_slow(struct page_pool *pool,
> if (unlikely(pp_order))
> return __page_pool_alloc_page_order(pool, gfp);
>
> /* Unnecessary as alloc cache is empty, but guarantees zero count */
> - if (unlikely(pool->alloc.count > 0))
> + if (unlikely(pool->alloc.count > 0)) // ^^^^^^^^^^^^^^^^^^^^^^
> return pool->alloc.cache[--pool->alloc.count];
>
> /* Mark empty alloc.cache slots "empty" for alloc_pages_bulk_array
> */
> memset(&pool->alloc.cache, 0, sizeof(void *) * bulk);
>
> + /* bulk API ret value also count existing pages, but array is empty
> */
> nr_pages = alloc_pages_bulk_array(gfp, bulk, pool->alloc.cache);
> if (unlikely(!nr_pages))
> return NULL;
>
> /* Pages have been filled into alloc.cache array, but count is zero
> and
> * page element have not been (possibly) DMA mapped.
> */
> - for (i = 0; i < nr_pages; i++) {
> + for (i = pool->alloc.count; i < nr_pages; i++) {
That last part would break as the loop is updating pool->alloc_count.
Just setting pool->alloc_count = nr_pages would break if PP_FLAG_DMA_MAP
was set and page_pool_dma_map failed. Right?
--
Mel Gorman
SUSE Labs
