From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (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 54AB52F22 for ; Mon, 22 Jan 2024 07:07:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705907227; cv=none; b=FsH0nHhHzJr2/YcQQdUB1fcjwQTc9CxL0HkHEMKOhXJd8Upw7UnZptuAhN/myYZj4j3Ef2EJrD+yqvIO77YMBi0Z8rKlC8Ksn2FiqSo+onVI1QWB6UFj1VE6FJemFGx1jbQzF0KQFAzsslA1OqLJ06zwvEVFmasDOWUOtQlg85Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705907227; c=relaxed/simple; bh=5TKqAWVs55lchICqxGsxk0ZeT7m9HqP3li9rplBM75g=; h=Message-ID:Subject:Date:From:To:Cc:References:In-Reply-To: Content-Type; b=H8s2Lu6y36L01Do71pYJ5tb6LENsiPjbq3W8zX+DeZlB3AQBqvLdUUJfD0zBbC93DXZVusnFo7O+Y2pBz6NwocOHTrJ8WPSO+/osDghq6HK6rnESf3bub7N63Mnueyau6sGT896L5xnreLmbvMuop3Vk/IlUhn8xU+HGiGTzUsM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; arc=none smtp.client-ip=115.124.30.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046049;MF=xuanzhuo@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0W.2pvmj_1705907214; Received: from localhost(mailfrom:xuanzhuo@linux.alibaba.com fp:SMTPD_---0W.2pvmj_1705907214) by smtp.aliyun-inc.com; Mon, 22 Jan 2024 15:06:55 +0800 Message-ID: <1705906930.2143333-5-xuanzhuo@linux.alibaba.com> Subject: Re: [PATCH 1/1] virtio_net: Add timeout handler to avoid kernel hang Date: Mon, 22 Jan 2024 15:02:10 +0800 From: Xuan Zhuo To: Jason Wang Cc: Andrew Lunn , Heng Qi , Paolo Abeni , Zhu Yanjun , mst@redhat.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, Zhu Yanjun References: <20240115012918.3081203-1-yanjun.zhu@intel.com> <667a9520-a53f-40a2-810a-6c1e45146589@linux.dev> <7dd89fc0-f31e-4f83-9c02-58ee67c2d436@linux.alibaba.com> <430b899c-aed4-419d-8ae8-544bb9bec5d9@lunn.ch> <64270652-8e0c-4db7-b245-b970d9588918@linux.dev> <1705895881.6990144-1-xuanzhuo@linux.alibaba.com> <1705904164.7020166-3-xuanzhuo@linux.alibaba.com> In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: On Mon, 22 Jan 2024 14:58:09 +0800, Jason Wang wrote: > On Mon, Jan 22, 2024 at 2:55=E2=80=AFPM Jason Wang = wrote: > > > > On Mon, Jan 22, 2024 at 2:20=E2=80=AFPM Xuan Zhuo wrote: > > > > > > On Mon, 22 Jan 2024 12:16:27 +0800, Jason Wang = wrote: > > > > On Mon, Jan 22, 2024 at 12:00=E2=80=AFPM Xuan Zhuo wrote: > > > > > > > > > > On Mon, 22 Jan 2024 11:14:30 +0800, Jason Wang wrote: > > > > > > On Mon, Jan 22, 2024 at 10:12=E2=80=AFAM Zhu Yanjun wrote: > > > > > > > > > > > > > > > > > > > > > =E5=9C=A8 2024/1/20 1:29, Andrew Lunn =E5=86=99=E9=81=93: > > > > > > > >>>>> while (!virtqueue_get_buf(vi->cvq, &tmp) && > > > > > > > >>>>> - !virtqueue_is_broken(vi->cvq)) > > > > > > > >>>>> + !virtqueue_is_broken(vi->cvq)) { > > > > > > > >>>>> + if (timeout) > > > > > > > >>>>> + timeout--; > > > > > > > >>>> This is not really a timeout, just a loop counter. 200 i= terations could > > > > > > > >>>> be a very short time on reasonable H/W. I guess this avo= id the soft > > > > > > > >>>> lockup, but possibly (likely?) breaks the functionality = when we need to > > > > > > > >>>> loop for some non negligible time. > > > > > > > >>>> > > > > > > > >>>> I fear we need a more complex solution, as mentioned by = Micheal in the > > > > > > > >>>> thread you quoted. > > > > > > > >>> Got it. I also look forward to the more complex solution = to this problem. > > > > > > > >> Can we add a device capability (new feature bit) such as c= trq_wait_timeout > > > > > > > >> to get a reasonable timeout=EF=BC=9F > > > > > > > > The usual solution to this is include/linux/iopoll.h. If yo= u can sleep > > > > > > > > read_poll_timeout() otherwise read_poll_timeout_atomic(). > > > > > > > > > > > > > > I read carefully the functions read_poll_timeout() and > > > > > > > read_poll_timeout_atomic(). The timeout is set by the caller = of the 2 > > > > > > > functions. > > > > > > > > > > > > FYI, in order to avoid a swtich of atomic or not, we need conve= rt rx > > > > > > mode setting to workqueue first: > > > > > > > > > > > > https://www.mail-archive.com/virtualization@lists.linux-foundat= ion.org/msg60298.html > > > > > > > > > > > > > > > > > > > > As such, can we add a module parameter to customize this time= out value > > > > > > > by the user? > > > > > > > > > > > > Who is the "user" here, or how can the "user" know the value? > > > > > > > > > > > > > > > > > > > > Or this timeout value is stored in device register, virtio_ne= t driver > > > > > > > will read this timeout value at initialization? > > > > > > > > > > > > See another thread. The design needs to be general, or you can = post a RFC. > > > > > > > > > > > > In another thought, we've already had a tx watchdog, maybe we c= an have > > > > > > something similar to cvq and use timeout + reset in that case. > > > > > > > > > > But we may block by the reset ^_^ if the device is broken? > > > > > > > > I mean vq reset here. > > > > > > I see. > > > > > > I mean when the deivce is broken, the vq reset also many be blocked. > > > > > > void vp_modern_set_queue_reset(struct virtio_pci_modern_devic= e *mdev, u16 index) > > > { > > > struct virtio_pci_modern_common_cfg __iomem *cfg; > > > > > > cfg =3D (struct virtio_pci_modern_common_cfg __iomem = *)mdev->common; > > > > > > vp_iowrite16(index, &cfg->cfg.queue_select); > > > vp_iowrite16(1, &cfg->queue_reset); > > > > > > while (vp_ioread16(&cfg->queue_reset)) > > > msleep(1); > > > > > > while (vp_ioread16(&cfg->cfg.queue_enable)) > > > msleep(1); > > > } > > > EXPORT_SYMBOL_GPL(vp_modern_set_queue_reset); > > > > > > In this function, for the broken device, we can not expect something. > > > > Yes, it's best effort, there's no guarantee then. But it doesn't harm t= o try. > > > > Thanks > > > > > > > > > > > > > > > > It looks like we have multiple goals here > > > > > > > > 1) avoid lockups, using workqueue + cond_resched() seems to be > > > > sufficient, it has issue but nothing new > > > > 2) recover from the unresponsive device, the issue for timeout is t= hat > > > > it needs to deal with false positives > > > > > > > > > I agree. > > > > > > But I want to add a new goal, cvq async. In the netdim, we will > > > send many requests via the cvq, so the cvq async will be nice. > > Then you need an interrupt for cvq. > > FYI, I've posted a series that use interrupt for cvq in the past: > > https://lore.kernel.org/lkml/6026e801-6fda-fee9-a69b-d06a80368621@redhat.= com/t/ I know this. But the interrupt maybe not a good solution without new space. > > Haven't found time in working on this anymore, maybe we can start from > this or not. I said async, but my aim is to put many requests to the cvq before getting = the response. Heng Qi posted this https://lore.kernel.org/all/1705410693-118895-4-git-sen= d-email-hengqi@linux.alibaba.com/ Thanks. > > Thanks > > > > > > > Thanks. > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > Thanks. > > > > > > > > > > > > > > > > > > > > > > Thans > > > > > > > > > > > > > > > > > > > > Zhu Yanjun > > > > > > > > > > > > > > > > > > > > > > > Andrew > > > > > > > > > > > > > > > > > > > > > > > > > >