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Fri, 20 Sep 2024 14:14:03 +0800 (CST) Received: from [10.67.120.129] (10.67.120.129) by dggpemf200006.china.huawei.com (7.185.36.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Fri, 20 Sep 2024 14:14:02 +0800 Message-ID: <2c5ccfff-6ab4-4aea-bff6-3679ff72cc9a@huawei.com> Date: Fri, 20 Sep 2024 14:14:02 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Ilias Apalodimas , Jesper Dangaard Brouer References: <20240918111826.863596-1-linyunsheng@huawei.com> <20240918111826.863596-3-linyunsheng@huawei.com> <894a3c2c-22f9-45b9-a82b-de7320066b42@kernel.org> <0e8c7a7a-0e2a-42ec-adbc-b29f6a514517@kernel.org> Content-Language: en-US From: Yunsheng Lin In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.120.129] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemf200006.china.huawei.com (7.185.36.61) X-Mailman-Original-Authentication-Results: smtp2.osuosl.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Subject: Re: [Intel-wired-lan] [PATCH net 2/2] page_pool: fix IOMMU crash when driver has already unbound X-BeenThere: intel-wired-lan@osuosl.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Wired Ethernet Linux Kernel Driver Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: imx@lists.linux.dev, Alexei Starovoitov , Alexander Duyck , linux-mm@kvack.org, Eric Dumazet , Tony Nguyen , Shenwei Wang , Ryder Lee , Leon Romanovsky , linux-rdma@vger.kernel.org, Przemek Kitszel , John Fastabend , IOMMU , liuyonglong@huawei.com, Clark Wang , zhangkun09@huawei.com, fanghaiqing@huawei.com, pabeni@redhat.com, Lorenzo Bianconi , Kalle Valo , Sean Wang , Wei Fang , kuba@kernel.org, Matthias Brugger , intel-wired-lan@lists.osuosl.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, AngeloGioacchino Del Regno , Daniel Borkmann , Robin Murphy , linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, Tariq Toukan , Alexander Lobakin , netdev@vger.kernel.org, linux-mediatek@lists.infradead.org, Andrew Morton , Shayne Chen , Saeed Mahameed , davem@davemloft.net, Felix Fietkau Errors-To: intel-wired-lan-bounces@osuosl.org Sender: "Intel-wired-lan" On 2024/9/20 13:29, Ilias Apalodimas wrote: > Hi Jesper, > > On Fri, 20 Sept 2024 at 00:04, Jesper Dangaard Brouer wrote: >> >> >> >> 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). 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 come back in page_pool_destroy(), which seems the same as the jakub's way from the viewpoint of user, and jakub's way seems more elegant than waiting in page_pool_destroy(). > > Keeping track of inflight packets that need to be unmapped is > certainly more complex. Delaying the netdevice destruction certainly > solves the problem but there's a huge cost IMHO. Those devices might > stay there forever and we have zero guarantees that the network stack > will eventually release (and unmap) those packets. What happens in > that case? The user basically has to reboot the entire machine, just > because he tries to bring an interface down and up again. Yes. The problem seems to be how long page_pool is allowed to stall the driver unloading? Does the driver unload stalling affect some feature like device hotplug? As the problem in [1], the stall might be forever due to caching in the network stack as discussed in [2], and there might be some other caching we don't know yet. The stalling log in [1] is caused by the caching in skb_attempt_defer_free(), we may argue that a timeout is needed for those kind of caching, but Eric seemed to think otherwise in commit log of [3]: "As Eric pointed out/predicted there's no guarantee that applications will read / close their sockets so a page pool page may be stuck in a socket (but not leaked) forever." 1. https://lore.kernel.org/netdev/20240814075603.05f8b0f5@kernel.org/T/#me2f2c89fbeb7f92a27d54a85aab5527efedfe260 2. https://lore.kernel.org/netdev/20240814075603.05f8b0f5@kernel.org/T/#m2687f25537395401cd6a810ac14e0e0d9addf97e 3. https://lore.kernel.org/netdev/ZWfuyc13oEkp583C@makrotopia.org/T/ > > Thanks > /Ilias >> >> >>> If no, it seems that the problem is still existed when the driver for >>> the device has unbound after device_del() is called.