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

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Message-ID: <20240923175226.GC9634@ziepe.ca>
Date: Mon, 23 Sep 2024 14:52:26 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Yunsheng Lin <linyunsheng@...wei.com>
Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>, 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>,
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	Sean Wang <sean.wang@...iatek.com>, Kalle Valo <kvalo@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
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	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,
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	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 Fri, Sep 20, 2024 at 02:14:02PM +0800, Yunsheng Lin wrote:

> I am not sure what dose the API that allows netdev to "give" struct device
> to page_pool look like or how to implement the API yet, but the obvious way
> to stall the calling of device_del() is to wait for the inflight
> page to

It is not device_del() you need to stall, but the remove() function of
the device driver.

Once all drivers have been unbound the DMA API can be reconfigured and
all existing DMA mappings must be concluded before this happens,
otherwise there will be problems.

So, stalling something like unregister_netdevice() would be a better
target - though stalling forever on driver unbind would not be
acceptable.

Jason