Re: [RFC PATCH v3 04/12] netdev: support binding dma-buf to netdevice

[Yunsheng Lin]

On 2023/11/8 5:59, Mina Almasry wrote:
> On Mon, Nov 6, 2023 at 11:46 PM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:
>>
>> On 2023/11/6 10:44, Mina Almasry wrote:
>>> +
>>> +void __netdev_devmem_binding_free(struct netdev_dmabuf_binding *binding)
>>> +{
>>> +     size_t size, avail;
>>> +
>>> +     gen_pool_for_each_chunk(binding->chunk_pool,
>>> +                             netdev_devmem_free_chunk_owner, NULL);
>>> +
>>> +     size = gen_pool_size(binding->chunk_pool);
>>> +     avail = gen_pool_avail(binding->chunk_pool);
>>> +
>>> +     if (!WARN(size != avail, "can't destroy genpool. size=%lu, avail=%lu",
>>> +               size, avail))
>>> +             gen_pool_destroy(binding->chunk_pool);
>>
>>
>> Is there any other place calling the gen_pool_destroy() when the above
>> warning is triggered? Do we have a leaking for binding->chunk_pool?
>>
> 
> gen_pool_destroy BUG_ON() if it's not empty at the time of destroying.
> Technically that should never happen, because
> __netdev_devmem_binding_free() should only be called when the refcount
> hits 0, so all the chunks have been freed back to the gen_pool. But,
> just in case, I don't want to crash the server just because I'm
> leaking a chunk... this is a bit of defensive programming that is
> typically frowned upon, but the behavior of gen_pool is so severe I
> think the WARN() + check is warranted here.

It seems it is pretty normal for the above to happen nowadays because of
retransmits timeouts, NAPI defer schemes mentioned below:

https://lkml.kernel.org/netdev/168269854650.2191653.8465259808498269815.stgit@firesoul/

And currently page pool core handles that by using a workqueue.