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23 Jun 2020 00:43:24 +0000 Received: from EX13MTAUWC001.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan2.pdx.amazon.com [10.170.41.162]) by email-inbound-relay-2c-c6afef2e.us-west-2.amazon.com (Postfix) with ESMTPS id 9574BA2519; Tue, 23 Jun 2020 00:43:23 +0000 (UTC) Received: from EX13D05UWC003.ant.amazon.com (10.43.162.226) by EX13MTAUWC001.ant.amazon.com (10.43.162.135) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 23 Jun 2020 00:43:14 +0000 Received: from EX13MTAUWC001.ant.amazon.com (10.43.162.135) by EX13D05UWC003.ant.amazon.com (10.43.162.226) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 23 Jun 2020 00:43:14 +0000 Received: from dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com (172.22.96.68) by mail-relay.amazon.com (10.43.162.232) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Tue, 23 Jun 2020 00:43:14 +0000 Received: by dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com (Postfix, from userid 4335130) id 1816D40359; Tue, 23 Jun 2020 00:43:14 +0000 (UTC) Date: Tue, 23 Jun 2020 00:43:14 +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" Message-ID: <20200623004314.GA28586@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> <20200617083528.GW735@Air-de-Roger> <20200619234312.GA24846@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <20200622083846.GF735@Air-de-Roger> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline In-Reply-To: <20200622083846.GF735@Air-de-Roger> User-Agent: Mutt/1.5.21 (2010-09-15) X-Rspamd-Queue-Id: 1ED07100D1C54 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 Mon, Jun 22, 2020 at 10:38:46AM +0200, Roger Pau Monn=E9 wrote: > CAUTION: This email originated from outside of the organization. Do not= click links or open attachments unless you can confirm the sender and kn= ow the content is safe. >=20 >=20 >=20 > On Fri, Jun 19, 2020 at 11:43:12PM +0000, Anchal Agarwal wrote: > > On Wed, Jun 17, 2020 at 10:35:28AM +0200, Roger Pau Monn=E9 wrote: > > > CAUTION: This email originated from outside of the organization. Do= not click links or open attachments unless you can confirm the sender an= d know the content is safe. > > > > > > > > > > > > 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=E9 wrote= : > > > > > CAUTION: This email originated from outside of the organization= . Do not click links or open attachments unless you can confirm the sende= r 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 organizat= ion. Do not click links or open attachments unless you can confirm the se= nder and know the content is safe. > > > > > > > + xenbus_dev_error(dev, err, "Freezing time= d out;" > > > > > > > + "the device may become i= nconsistent 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 atte= mpt to > > > > > > restore things to a working state. > > > > > > > > > > > > You mean if backend closed after timeout? Is there a way to k= now 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 ne= ed 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 o= rder to > > > > > try to reconnect to the backend when possible. > > > > > > > > > From what I understand forcing manually is, failing the freeze wi= thout > > > > disconnect and try to revive the connection by unfreezing the > > > > queues->reconnecting to backend [which never got diconnected]. Ma= y be even > > > > tearing down things manually because I am not sure what state wil= l frontend > > > > see if backend fails to to disconnect at any point in time. I ass= umed connected. > > > > Then again if its "CONNECTED" I may not need to tear down everyth= ing 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 x= en_blkif_disconnect fail, > > > > I don't see it getting handled in the backend then what will be b= ackend's state? > > > > Will it still switch xenbus state to 'Closed'? If not what will f= rontend see, > > > > if it tries to read backend's state through xenbus_read_driver_st= ate ? > > > > > > > > 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 EB= USY > > > > What will be state of backend here? > > > > > > Backend should stay in state 'Closing' then, until it can finish > > > tearing down. > > > > > It disconnects the ring after switching to connected state too. > > > > Frontend did not tear down the rings if backend does not s= witches the > > > > state to 'Closed' in case of failure. > > > > > > > > If backend stays in CONNECTED state, then even if we mark it Init= ialised in frontend, backend > > > > > > Backend will stay in state 'Closing' I think. > > > > > > > won't be calling connect(). {From reading code in frontend_change= d} > > > > IMU, Initialising will fail since backend dev->state !=3D XenbusS= tateClosed plus > > > > we did not tear down anything so calling talk_to_blkback may not = be needed > > > > > > > > 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. > > > > > It does not seems to work correctly, I get hung tasks all over and al= l the > > requests to filesystem gets stuck. Backend does shows the state as co= nnected > > after xenbus_dev_suspend fails but I think there may be something mis= sing. > > I don't seem to get IO interrupts thereafter i.e hitting the function= blkif_interrupts. > > I think just marking it initialised may not be the only thing. > > Here is a short description of what I am trying to do: > > So, on timeout: > > Switch XenBusState to "Initialized" > > unquiesce/unfreeze the queues and return > > mark info->connected =3D BLKIF_STATE_CONNECTED >=20 > If xenbus state is Initialized isn't it wrong to set info->connected > =3D=3D CONNECTED? > Yes, you are right earlier I was marking it explicitly but that was not r= ight, the connect path for blkfront will do that. > You should tear down all the internal state (like a proper close)? >=20 Isn't that similar to disconnecting in the first place that failed during freeze? Do you mean re-try to close but this time re-connect after close basically do everything you would at "restore"? Also, I experimented with that and it works intermittently. I want to tak= e a step back on this issue and ask few questions here: 1. Is fixing this recovery a blocker for me sending in a V2 version? 2. In our 2-3 years of supporting this feature at large scale we haven't = seen this issue where backend fails to disconnect. What we are trying to do here is creat= e a hypothetical situation where we leave backend in Closing state and try an= d see how it recovers. The reason why I think it "may not" occur and the timeout of 5H= Z is sufficient is because we haven't come across even a single use-case where= it caused hibernation to fail. The reason why I think "it may" occur is if we are running a really memor= y intensive workload and ring is busy and is unable to complete all the req= uests in the given timeout. This is very unlikely though. 3) Also, I do not think this may be straight forward to fix and expect hibernation to work flawlessly in subsequent invocations. I am open to=20 all suggestions. Thanks, Anchal > > return EBUSY > > > > I even allowed blkfront_connect to switch state to "CONNECTED" rather= me doing > > it explicitly as mentioned above without re-allocating/re-registering= the device > > just to make sure bklfront_info object has all the right values. > > Do you see anythign missing here? >=20 > I'm afraid you will have to do a little bit of debugging here to > figure out what's going on. You can add printk's to several places to > see which path is taken, and why blkfront ends in such state. > > Thanks, Roger.