Re: [PATCH net] page_pool: Fix use-after-free in page_pool_recycle_in_ring

[Yunsheng Lin <linyunsheng@huawei.com>]

On 2025/5/23 14:45, Dong Chenchen wrote:

>  
>  static bool page_pool_recycle_in_ring(struct page_pool *pool, netmem_ref netmem)
>  {
> +	bool in_softirq;
>  	int ret;
int -> bool?

>  	/* BH protection not needed if current is softirq */
> -	if (in_softirq())
> -		ret = ptr_ring_produce(&pool->ring, (__force void *)netmem);
> -	else
> -		ret = ptr_ring_produce_bh(&pool->ring, (__force void *)netmem);
> -
> -	if (!ret) {
> +	in_softirq = page_pool_producer_lock(pool);
> +	ret = !__ptr_ring_produce(&pool->ring, (__force void *)netmem);
> +	if (ret)
>  		recycle_stat_inc(pool, ring);
> -		return true;
> -	}
> +	page_pool_producer_unlock(pool, in_softirq);
>  
> -	return false;
> +	return ret;
>  }
>  
>  /* Only allow direct recycling in special circumstances, into the
> @@ -1091,10 +1088,14 @@ static void page_pool_scrub(struct page_pool *pool)
>  
>  static int page_pool_release(struct page_pool *pool)
>  {
> +	bool in_softirq;
>  	int inflight;
>  
>  	page_pool_scrub(pool);
>  	inflight = page_pool_inflight(pool, true);
> +	/* Acquire producer lock to make sure producers have exited. */
> +	in_softirq = page_pool_producer_lock(pool);
> +	page_pool_producer_unlock(pool, in_softirq);

Is a compiler barrier needed to ensure compiler doesn't optimize away
the above code?

>  	if (!inflight)
>  		__page_pool_destroy(pool);
>