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

[Yunsheng Lin <linyunsheng@huawei.com>]

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

> 
> --Jesper