Re: [PATCH net-next] page pool: not return page to alloc cache during pool destruction

[Yunsheng Lin]

On 2023/6/15 9:36, Liang Chen wrote:
> When destroying a page pool, the alloc cache and recycle ring are emptied.
> If there are inflight pages, the retry process will periodically check the
> recycle ring for recently returned pages, but not the alloc cache (alloc
> cache is only emptied once). As a result, any pages returned to the alloc
> cache after the page pool destruction will be stuck there and cause the
> retry process to continuously look for inflight pages and report warnings.

It seems there is still page_pool_put[_full]_page() called with
allow_direct being true after page_pool_destroy() is call, which
is not allowed.

Normally the driver will call napi_disable() before
page_pool_destroy() to ensure there is no such page_pool_destroy()
calling with allow_direct being true after page_pool_destroy() is
called.

> 
> To safeguard against this situation, any pages returning to the alloc cache
> after pool destruction should be prevented.
> 
> Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx>
> ---
>  net/core/page_pool.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index a3e12a61d456..76255313d349 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -595,7 +595,7 @@ __page_pool_put_page(struct page_pool *pool, struct page *page,
>  			page_pool_dma_sync_for_device(pool, page,
>  						      dma_sync_size);
>  
> -		if (allow_direct && in_softirq() &&
> +		if (allow_direct && in_softirq() && !pool->destroy_cnt &&

The checking seems racy when  __page_pool_put_page() and
page_pool_destroy() are called concurently.

>  		    page_pool_recycle_in_cache(page, pool))
>  			return NULL;
>  
>