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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 0F7D5C433E1 for ; Wed, 17 Jun 2020 08:35:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D1E962073E for ; Wed, 17 Jun 2020 08:35:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D1E962073E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=citrix.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 721916B0008; Wed, 17 Jun 2020 04:35:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6D21C6B000D; Wed, 17 Jun 2020 04:35:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5995E6B000E; Wed, 17 Jun 2020 04:35:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0185.hostedemail.com [216.40.44.185]) by kanga.kvack.org (Postfix) with ESMTP id 423B76B0008 for ; Wed, 17 Jun 2020 04:35:43 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id AA32E181AC9BF for ; Wed, 17 Jun 2020 08:35:42 +0000 (UTC) X-FDA: 76938045324.08.hole02_630e6b126e06 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id 7B9F01819E764 for ; Wed, 17 Jun 2020 08:35:42 +0000 (UTC) X-HE-Tag: hole02_630e6b126e06 X-Filterd-Recvd-Size: 6514 Received: from esa2.hc3370-68.iphmx.com (esa2.hc3370-68.iphmx.com [216.71.145.153]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Wed, 17 Jun 2020 08:35:41 +0000 (UTC) Authentication-Results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none IronPort-SDR: KfZvMvC1oYnZ7gi+KDWOviH4clxbHShSY7Yli+xfkrqN6LkJMaGowI1WLqHxqcACgMUrxfkUAD Ay5pg5WGOeqKL0CCypgK4qhxMgOHjyTIf64e1aNhYRAm71VGxZrK78hisJYBoO7fnRxdMgfY7b vDubhXWnqwLSYTQ7ryxlfakGFVKT1POd8dRmcMBv35hFYrPvNJEhPlc4qaSrLIUxHxgq6p86dI Fvz6UQo69l4R4knwvEj6X3MlFh19OkyWqWkPIwHX3MDCwr+2pRlebLitMY4MMI8I/Szkk6yaRS 9UE= X-SBRS: 2.7 X-MesageID: 20261029 X-Ironport-Server: esa2.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.73,522,1583211600"; d="scan'208";a="20261029" Date: Wed, 17 Jun 2020 10:35:28 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Anchal Agarwal 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: <20200617083528.GW735@Air-de-Roger> 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="utf-8" Content-Disposition: inline In-Reply-To: <20200616214925.GA21684@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To AMSPEX02CL02.citrite.net (10.69.22.126) X-Rspamd-Queue-Id: 7B9F01819E764 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 Monn=C3=A9 wrote: > > CAUTION: This email originated from outside of the organization. Do n= ot click links or open attachments unless you can confirm the sender and = know the content is safe. > > On Wed, Jun 03, 2020 at 11:33:52PM +0000, Agarwal, Anchal wrote: > > > CAUTION: This email originated from outside of the organization. D= o not click links or open attachments unless you can confirm the sender a= nd know the content is safe. > > > > + xenbus_dev_error(dev, err, "Freezing timed out;= " > > > > + "the device may become inconsi= stent state"); > > > > > > Leaving the device in this state is quite bad, as it's in a clo= sed > > > 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 th= at? 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 d= idn'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. > >=20 > > 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 t= o > > try to reconnect to the backend when possible. > >=20 > 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 e= ven > tearing down things manually because I am not sure what state will fron= tend > see if backend fails to to disconnect at any point in time. I assumed c= onnected. > Then again if its "CONNECTED" I may not need to tear down everything an= d start > from Initialising state because that may not work. >=20 > So I am not so sure about backend's state so much, lets say if xen_blk= if_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 fronten= d see,=20 > if it tries to read backend's state through xenbus_read_driver_state ? >=20 > 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? Backend should stay in state 'Closing' then, until it can finish tearing down. > Frontend did not tear down the rings if backend does not switche= s the > state to 'Closed' in case of failure. >=20 > If backend stays in CONNECTED state, then even if we mark it Initialise= d in frontend, backend Backend will stay in state 'Closing' I think. > won't be calling connect(). {From reading code in frontend_changed} > IMU, Initialising will fail since backend dev->state !=3D XenbusStateCl= osed plus > we did not tear down anything so calling talk_to_blkback may not be nee= ded >=20 > Does that sound correct? I think switching to the initial state in order to try to attempt a reconnection would be our best bet here. Thanks, Roger.