From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AC9EFC433DF for ; Tue, 16 Jun 2020 22:31:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DEA8207D3 for ; Tue, 16 Jun 2020 22:31:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="HydIri+6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726403AbgFPWa7 (ORCPT ); Tue, 16 Jun 2020 18:30:59 -0400 Received: from smtp-fw-6001.amazon.com ([52.95.48.154]:20525 "EHLO smtp-fw-6001.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725849AbgFPWa6 (ORCPT ); Tue, 16 Jun 2020 18:30:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1592346656; x=1623882656; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=/5Ov+gppYN7KJ5aQn25HOqJLUAtFPPVAyop7Fexu5eI=; b=HydIri+69QqYVrfQMhu7WQHXisg0S9+aHXTLmvwgGxYKQl9GBQ8KPyth QIImQLWGLmAEobj7Ay8UN5iwBQwhRs20ZQ+adVZQ+U79jPOVuTKOVoZiO cu+dFC6jEyVlIwej4VyU2esY0CR2XIaJFkdIoTLPTsqGMx8pp5PLA2SBB s=; IronPort-SDR: 0wp0vaMsG06ZplyB+5A5c/qT8EcLICE9E/lPyLBASpFVCVcIdV45ygLSeUw2A92LeT7u282MWJ LMXVSzXi0/BQ== X-IronPort-AV: E=Sophos;i="5.73,520,1583193600"; d="scan'208";a="38021711" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-2a-53356bf6.us-west-2.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-6001.iad6.amazon.com with ESMTP; 16 Jun 2020 22:30:53 +0000 Received: from EX13MTAUWB001.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan2.pdx.amazon.com [10.170.41.162]) by email-inbound-relay-2a-53356bf6.us-west-2.amazon.com (Postfix) with ESMTPS id 77B67A1F74; Tue, 16 Jun 2020 22:30:50 +0000 (UTC) Received: from EX13D01UWB002.ant.amazon.com (10.43.161.136) by EX13MTAUWB001.ant.amazon.com (10.43.161.207) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 16 Jun 2020 22:30:03 +0000 Received: from EX13MTAUWB001.ant.amazon.com (10.43.161.207) by EX13d01UWB002.ant.amazon.com (10.43.161.136) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 16 Jun 2020 22:30:03 +0000 Received: from dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com (172.22.96.68) by mail-relay.amazon.com (10.43.161.249) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Tue, 16 Jun 2020 22:30:03 +0000 Received: by dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com (Postfix, from userid 4335130) id 3892B40139; Tue, 16 Jun 2020 22:30:03 +0000 (UTC) Date: Tue, 16 Jun 2020 22:30:03 +0000 From: Anchal Agarwal To: Roger Pau =?iso-8859-1?Q?Monn=E9?= CC: Boris Ostrovsky , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "hpa@zytor.com" , "x86@kernel.org" , "jgross@suse.com" , "linux-pm@vger.kernel.org" , "linux-mm@kvack.org" , "Kamata, Munehisa" , "sstabellini@kernel.org" , "konrad.wilk@oracle.com" , "axboe@kernel.dk" , "davem@davemloft.net" , "rjw@rjwysocki.net" , "len.brown@intel.com" , "pavel@ucw.cz" , "peterz@infradead.org" , "Valentin, Eduardo" , "Singh, Balbir" , "xen-devel@lists.xenproject.org" , "vkuznets@redhat.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Woodhouse, David" , "benh@kernel.crashing.org" Subject: Re: [PATCH 06/12] xen-blkfront: add callbacks for PM suspend and hibernation] Message-ID: <20200616223003.GA28769@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> References: <7FD7505E-79AA-43F6-8D5F-7A2567F333AB@amazon.com> <20200604070548.GH1195@Air-de-Roger> <20200616214925.GA21684@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200616214925.GA21684@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 16, 2020 at 09:49:25PM +0000, Anchal Agarwal wrote: > On Thu, Jun 04, 2020 at 09:05:48AM +0200, Roger Pau Monné wrote: > > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. > > > > > > > > Hello, > > > > On Wed, Jun 03, 2020 at 11:33:52PM +0000, Agarwal, Anchal wrote: > > > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. > > > > > > > > > > > > On Tue, May 19, 2020 at 11:27:50PM +0000, Anchal Agarwal wrote: > > > > From: Munehisa Kamata > > > > > > > > S4 power transition states are much different than xen > > > > suspend/resume. Former is visible to the guest and frontend drivers should > > > > be aware of the state transitions and should be able to take appropriate > > > > actions when needed. In transition to S4 we need to make sure that at least > > > > all the in-flight blkif requests get completed, since they probably contain > > > > bits of the guest's memory image and that's not going to get saved any > > > > other way. Hence, re-issuing of in-flight requests as in case of xen resume > > > > will not work here. This is in contrast to xen-suspend where we need to > > > > freeze with as little processing as possible to avoid dirtying RAM late in > > > > the migration cycle and we know that in-flight data can wait. > > > > > > > > Add freeze, thaw and restore callbacks for PM suspend and hibernation > > > > support. All frontend drivers that needs to use PM_HIBERNATION/PM_SUSPEND > > > > events, need to implement these xenbus_driver callbacks. The freeze handler > > > > stops block-layer queue and disconnect the frontend from the backend while > > > > freeing ring_info and associated resources. Before disconnecting from the > > > > backend, we need to prevent any new IO from being queued and wait for existing > > > > IO to complete. Freeze/unfreeze of the queues will guarantee that there are no > > > > requests in use on the shared ring. However, for sanity we should check > > > > state of the ring before disconnecting to make sure that there are no > > > > outstanding requests to be processed on the ring. The restore handler > > > > re-allocates ring_info, unquiesces and unfreezes the queue and re-connect to > > > > the backend, so that rest of the kernel can continue to use the block device > > > > transparently. > > > > > > > > Note:For older backends,if a backend doesn't have commit'12ea729645ace' > > > > xen/blkback: unmap all persistent grants when frontend gets disconnected, > > > > the frontend may see massive amount of grant table warning when freeing > > > > resources. > > > > [ 36.852659] deferring g.e. 0xf9 (pfn 0xffffffffffffffff) > > > > [ 36.855089] xen:grant_table: WARNING:e.g. 0x112 still in use! > > > > > > > > In this case, persistent grants would need to be disabled. > > > > > > > > [Anchal Changelog: Removed timeout/request during blkfront freeze. > > > > Reworked the whole patch to work with blk-mq and incorporate upstream's > > > > comments] > > > > > > Please tag versions using vX and it would be helpful if you could list > > > the specific changes that you performed between versions. There where > > > 3 RFC versions IIRC, and there's no log of the changes between them. > > > > > > I will elaborate on "upstream's comments" in my changelog in my next round of patches. > > > > Sorry for being picky, but can you please make sure your email client > > properly quotes previous emails on reply. Note the lack of '>' added > > to the quoted parts of your reply. > That was just my outlook probably. Note taken. > > > > > > + } > > > > + > > > > break; > > > > + } > > > > + > > > > + /* > > > > + * We may somehow receive backend's Closed again while thawing > > > > + * or restoring and it causes thawing or restoring to fail. > > > > + * Ignore such unexpected state regardless of the backend state. > > > > + */ > > > > + if (info->connected == BLKIF_STATE_FROZEN) { > > > > > > I think you can join this with the previous dev->state == XenbusStateClosed? > > > > > > Also, won't the device be in the Closed state already if it's in state > > > frozen? > > > Yes but I think this mostly due to a hypothetical case if during thawing backend switches to Closed state. > > > I am not entirely sure if that could happen. Could use some expertise here. > > > > I think the frontend seeing the backend in the closed state during > > restore would be a bug that should prevent the frontend from > > resuming. > > > > > > + /* Kick the backend to disconnect */ > > > > + xenbus_switch_state(dev, XenbusStateClosing); > > > > + > > > > + /* > > > > + * We don't want to move forward before the frontend is diconnected > > > > + * from the backend cleanly. > > > > + */ > > > > + timeout = wait_for_completion_timeout(&info->wait_backend_disconnected, > > > > + timeout); > > > > + if (!timeout) { > > > > + err = -EBUSY; > > > > > > Note err is only used here, and I think could just be dropped. > > > > > > This err is what's being returned from the function. Am I missing anything? > > > > Just 'return -EBUSY;' directly, and remove the top level variable. You > > can also use -EBUSY directly in the xenbus_dev_error call. Anyway, not > > that important. > > > > > > + xenbus_dev_error(dev, err, "Freezing timed out;" > > > > + "the device may become inconsistent state"); > > > > > > Leaving the device in this state is quite bad, as it's in a closed > > > state and with the queues frozen. You should make an attempt to > > > restore things to a working state. > > > > > > You mean if backend closed after timeout? Is there a way to know that? I understand it's not good to > > > leave it in this state however, I am still trying to find if there is a good way to know if backend is still connected after timeout. > > > Hence the message " the device may become inconsistent state". I didn't see a timeout not even once on my end so that's why > > > I may be looking for an alternate perspective here. may be need to thaw everything back intentionally is one thing I could think of. > > > > You can manually force this state, and then check that it will behave > > correctly. I would expect that on a failure to disconnect from the > > backend you should switch the frontend to the 'Init' state in order to > > try to reconnect to the backend when possible. > > > From what I understand forcing manually is, failing the freeze without > disconnect and try to revive the connection by unfreezing the > queues->reconnecting to backend [which never got diconnected]. May be even > tearing down things manually because I am not sure what state will frontend > see if backend fails to to disconnect at any point in time. I assumed connected. > Then again if its "CONNECTED" I may not need to tear down everything and start > from Initialising state because that may not work. > > So I am not so sure about backend's state so much, lets say if xen_blkif_disconnect fail, > I don't see it getting handled in the backend then what will be backend's state? > Will it still switch xenbus state to 'Closed'? If not what will frontend see, > if it tries to read backend's state through xenbus_read_driver_state ? > > So the flow be like: > Front end marks XenbusStateClosing > Backend marks its state as XenbusStateClosing > Frontend marks XenbusStateClosed > Backend disconnects calls xen_blkif_disconnect > Backend fails to disconnect, the above function returns EBUSY > What will be state of backend here? > Frontend did not tear down the rings if backend does not switches the > state to 'Closed' in case of failure. > > If backend stays in CONNECTED state, then even if we mark it Initialised in frontend, backend > won't be calling connect(). {From reading code in frontend_changed} > IMU, Initialising will fail since backend dev->state != XenbusStateClosed plus > we did not tear down anything so calling talk_to_blkback may not be needed > > Does that sound correct? Send that too quickly, I also meant to add XenBusIntialised state should be ok only if we expect backend will stay in "Connected" state. Also, I experimented with that notion. I am little worried about the correctness here. Can the backend come to an Unknown state somehow? > > > > + } > > > > + > > > > + return err; > > > > +} > > > > + > > > > +static int blkfront_restore(struct xenbus_device *dev) > > > > +{ > > > > + struct blkfront_info *info = dev_get_drvdata(&dev->dev); > > > > + int err = 0; > > > > + > > > > + err = talk_to_blkback(dev, info); > > > > + blk_mq_unquiesce_queue(info->rq); > > > > + blk_mq_unfreeze_queue(info->rq); > > > > + if (!err) > > > > + blk_mq_update_nr_hw_queues(&info->tag_set, info->nr_rings); > > > > > > Bad indentation. Also shouldn't you first update the queues and then > > > unfreeze them? > > > Please correct me if I am wrong, blk_mq_update_nr_hw_queues freezes the queue > > > So I don't think the order could be reversed. > > > > Regardless of what blk_mq_update_nr_hw_queues does, I don't think it's > > correct to unfreeze the queues without having updated them. Also the > > freezing/unfreezing uses a refcount, so I think it's perfectly fine to > > call blk_mq_update_nr_hw_queues first and then unfreeze the queues. > > > > Also note that talk_to_blkback returning an error should likely > > prevent any unfreezing, as the queues won't be updated to match the > > parameters of the backend. > > > I think you are right here. Will send out fixes in V2 > > Thanks, Roger. > > > Thanks, > Anchal >