From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A8D31CF8B; Fri, 20 Sep 2024 06:30:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726813854; cv=none; b=cnAZ3rRZtfA8jSChjAm2tAFDU2nhxeqN4oWGL2jYxElUJtsQsEotmZU5O50/g94iMA4TitPWL0IeaQEYFLYN7xIetbqTXLDDVC3Rj70S9x1eJGhd9h8AO03dJMgAgyyKxqQDBQ4dHeBsbbNRuczwgtDlHAAWEPzeSdsYO02cT9E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726813854; c=relaxed/simple; bh=pUsj6zi6XSx6GhIlGdt1Hl9sG+23RLjq3jnloPOfGSA=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=rxDIsaTHi3kWq43/mRml/2YUdB9q/6XVJyZcbfYOnOEMi1uTbtpezOSHa3YNGc6CcCZyVewtNvSv5//QyWFnKLfJDN3h10xzcg5k4JcqMR5i+r+6fvsULmxIW4EO156J0uVbl2awpoEm+AurSY7y6NuNUYqBNzrEVDMBFLfNbtg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.162.112]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4X92BV2t0Fz2DcJj; Fri, 20 Sep 2024 14:13:22 +0800 (CST) Received: from dggpemf200006.china.huawei.com (unknown [7.185.36.61]) by mail.maildlp.com (Postfix) with ESMTPS id 140801401DC; 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 Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 2/2] page_pool: fix IOMMU crash when driver has already unbound To: Ilias Apalodimas , Jesper Dangaard Brouer CC: , , , , , , Robin Murphy , Alexander Duyck , IOMMU , Wei Fang , Shenwei Wang , Clark Wang , Eric Dumazet , Tony Nguyen , Przemek Kitszel , Alexander Lobakin , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Saeed Mahameed , Leon Romanovsky , Tariq Toukan , Felix Fietkau , Lorenzo Bianconi , Ryder Lee , Shayne Chen , Sean Wang , Kalle Valo , Matthias Brugger , AngeloGioacchino Del Regno , Andrew Morton , , , , , , , , , , 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-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemf200006.china.huawei.com (7.185.36.61) 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.