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

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Message-ID: <894a3c2c-22f9-45b9-a82b-de7320066b42@kernel.org>
Date: Thu, 19 Sep 2024 11:42:40 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Ilias Apalodimas <ilias.apalodimas@...aro.org>,
 Yunsheng Lin <linyunsheng@...wei.com>
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 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?

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?

--Jesper