Re: [BUG Report] KASAN: slab-use-after-free in page_pool_recycle_in_ring

["dongchenchen (A)" <dongchenchen2@huawei.com>]

> On Thu, 22 May 2025 23:17:32 +0800 dongchenchen (A) wrote:
>> Hi, Jakub
>> Maybe we can fix the problem as follow:
> Yes! a couple of minor nit picks below..
>
>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>> index 7745ad924ae2..de3fa33d6775 100644
>> --- a/net/core/page_pool.c
>> +++ b/net/core/page_pool.c
>> @@ -707,19 +707,18 @@ void page_pool_return_page(struct page_pool *pool, netmem_ref netmem)
>>    
>>    static bool page_pool_recycle_in_ring(struct page_pool *pool, netmem_ref netmem)
>>    {
>> +	bool in_softirq;
>>    	int ret;
>> -	/* 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) {
>> +	/* BH protection not needed if current is softirq */
>> +	in_softirq = page_pool_producer_lock(pool);
>> +	ret = __ptr_ring_produce(&pool->ring, (__force void *)netmem);
> Maybe we can flip the return value here we won't have to negate it below
> and at return? Like this:
>
> 	ret = !__ptr_ring_produce(&pool->ring, (__force void *)netmem);
>
> and adjust subsequent code

Hi,Jakub
Thanks for your suggestions!

>> +	if (!ret)
>>    		recycle_stat_inc(pool, ring);
>> -		return true;
>> -	}
>>    
>> -	return false;
>> +	page_pool_producer_unlock(pool, in_softirq);
>> +
>> +	return ret ? false : true;
>>    }
>>    
>>    /* Only allow direct recycling in special circumstances, into the
>>
>> @@ -1091,10 +1090,16 @@ static void page_pool_scrub(struct page_pool *pool)
>>    
>>    static int page_pool_release(struct page_pool *pool)
>>    {
>> +	bool in_softirq;
>>    	int inflight;
>>    
>> +	/* Acquire producer lock to make sure we don't race with another thread
>> +	 * returning a netmem to the ptr_ring.
>> +	 */
>> +	in_softirq = page_pool_producer_lock(pool);
>>    	page_pool_scrub(pool);
>>    	inflight = page_pool_inflight(pool, true);
>> +	page_pool_producer_unlock(pool, in_softirq);
> As I suggested earlier we don't have to lock the consumer, taking both
> locks has lock ordering implications. My preference would be:
>
>    	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);

Yes! there is no need to hold lock for page_pool_inflight(). The lock can
be used as a barrier for the completion of the recycle process.
I have tested this patch. The patch will be sent later.
----- Best Regards,
Dong Chenchen