netdev - Re: [PATCH net-next v5 2/2] page_pool: Track DMA-mapped pages and unmap them when destroying the pool

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Message-ID: <aaf31c50-9b57-40b7-bbd7-e19171370563@intel.com>
Date: Mon, 31 Mar 2025 18:35:37 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>
CC: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>, Saeed Mahameed <saeedm@...dia.com>,
	Leon Romanovsky <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>, "Andrew
 Lunn" <andrew+netdev@...n.ch>, Eric Dumazet <edumazet@...gle.com>, Paolo
 Abeni <pabeni@...hat.com>, Ilias Apalodimas <ilias.apalodimas@...aro.org>,
	"Simon Horman" <horms@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
	"Mina Almasry" <almasrymina@...gle.com>, Yonglong Liu
	<liuyonglong@...wei.com>, Yunsheng Lin <linyunsheng@...wei.com>, Pavel
 Begunkov <asml.silence@...il.com>, Matthew Wilcox <willy@...radead.org>,
	<netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
	<linux-rdma@...r.kernel.org>, <linux-mm@...ck.org>, Qiuling Ren
	<qren@...hat.com>, Yuying Ma <yuma@...hat.com>
Subject: Re: [PATCH net-next v5 2/2] page_pool: Track DMA-mapped pages and
 unmap them when destroying the pool

From: Toke Høiland-Jørgensen <toke@...hat.com>
Date: Fri, 28 Mar 2025 13:19:09 +0100

> When enabling DMA mapping in page_pool, pages are kept DMA mapped until
> they are released from the pool, to avoid the overhead of re-mapping the
> pages every time they are used. This causes resource leaks and/or
> crashes when there are pages still outstanding while the device is torn
> down, because page_pool will attempt an unmap through a non-existent DMA
> device on the subsequent page return.

[...]

> @@ -173,10 +212,10 @@ struct page_pool {
>  	int cpuid;
>  	u32 pages_state_hold_cnt;
>  
> -	bool has_init_callback:1;	/* slow::init_callback is set */
> +	bool dma_sync;			/* Perform DMA sync for device */

Have you seen my comment under v3 (sorry but I missed that there was v4
already)? Can't we just test the bit atomically?

>  	bool dma_map:1;			/* Perform DMA mapping */
> -	bool dma_sync:1;		/* Perform DMA sync for device */
>  	bool dma_sync_for_cpu:1;	/* Perform DMA sync for cpu */
> +	bool has_init_callback:1;	/* slow::init_callback is set */

Thanks,
Olek