Re: [PATCH net 2/2] page_pool: fix IOMMU crash when driver has already unbound

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 19/09/2024 13.15, Yunsheng Lin wrote:
> On 2024/9/19 17:42, Jesper Dangaard Brouer wrote:
>>
>> On 18/09/2024 19.06, Ilias Apalodimas wrote:
>>>> In order not to do the dma unmmapping after driver has already
>>>> unbound and stall the unloading of the networking driver, add
>>>> the pool->items array to record all the pages including the ones
>>>> which are handed over to network stack, so the page_pool can
>>>> do the dma unmmapping for those pages when page_pool_destroy()
>>>> is called.
>>>
>>> So, I was thinking of a very similar idea. But what do you mean by
>>> "all"? The pages that are still in caches (slow or fast) of the pool
>>> will be unmapped during page_pool_destroy().
>>
>> I really dislike this idea of having to keep track of all outstanding pages.
>>
>> I liked Jakub's idea of keeping the netdev around for longer.
>>
>> This is all related to destroying the struct device that have points to
>> the DMA engine, right?
> 
> Yes, the problem seems to be that when device_del() is called, there is
> no guarantee hw behind the 'struct device ' will be usable even if we
> call get_device() on it.
> 
>>
>> Why don't we add an API that allow netdev to "give" struct device to
>> page_pool.  And then the page_poll will take over when we can safely
>> free the stuct device?
> 
> By 'allow netdev to "give" struct device to page_pool', does it mean
> page_pool become the driver for the device?
> If yes, it seems that is similar to jakub's idea, as both seems to stall
> the calling of device_del() by not returning when the driver unloading.

Yes, this is what I mean. (That is why I mentioned Jakub's idea).


> If no, it seems that the problem is still existed when the driver for
> the device has unbound after device_del() is called.