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

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Message-ID: <0e8c7a7a-0e2a-42ec-adbc-b29f6a514517@kernel.org>
Date: Thu, 19 Sep 2024 23:04:43 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Yunsheng Lin <linyunsheng@...wei.com>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 liuyonglong@...wei.com, fanghaiqing@...wei.com, zhangkun09@...wei.com,
 Robin Murphy <robin.murphy@....com>,
 Alexander Duyck <alexander.duyck@...il.com>, IOMMU <iommu@...ts.linux.dev>,
 Wei Fang <wei.fang@....com>, Shenwei Wang <shenwei.wang@....com>,
 Clark Wang <xiaoning.wang@....com>, Eric Dumazet <edumazet@...gle.com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>, Saeed Mahameed
 <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Tariq Toukan <tariqt@...dia.com>, Felix Fietkau <nbd@....name>,
 Lorenzo Bianconi <lorenzo@...nel.org>, Ryder Lee <ryder.lee@...iatek.com>,
 Shayne Chen <shayne.chen@...iatek.com>, Sean Wang <sean.wang@...iatek.com>,
 Kalle Valo <kvalo@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Andrew Morton <akpm@...ux-foundation.org>, imx@...ts.linux.dev,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 intel-wired-lan@...ts.osuosl.org, bpf@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-wireless@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org,
 linux-mm@...ck.org
Subject: Re: [PATCH net 2/2] page_pool: fix IOMMU crash when driver has
 already unbound



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.