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Date:   Thu, 13 Sep 2018 17:08:00 +0200
From:   Roger Pau =?utf-8?B?TW9ubsOp?= <roger.pau@citrix.com>
To:     Valentin Vidic <Valentin.Vidic@CARNet.hr>
CC:     <drbd-user@lists.linbit.com>, Jens Axboe <axboe@kernel.dk>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        <linux-kernel@vger.kernel.org>, <stable@vger.kernel.org>,
        <linux-block@vger.kernel.org>, <xen-devel@lists.xenproject.org>
Subject: Re: [DRBD-user] [PATCH] xen-blkback: Switch to closed state after
 releasing the backing device
Message-ID: <20180913150800.haswzd7t2xccbgvl@mac.bytemobile.com>
References: <20180907120337.GB11834@soda.linbit>
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 <20180910124531.GA31737@soda.linbit>
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On Mon, Sep 10, 2018 at 06:18:31PM +0200, Valentin Vidic wrote:
> On Mon, Sep 10, 2018 at 05:00:58PM +0200, Roger Pau Monn? wrote:
> > I can try to take a look at this and attempt to make sure the state is
> > only changed to closed in blkback _after_ the device has been
> > released, but it might take me a couple of days to get you a patch.
> 
> Thanks, I have two test nodes now where I can try different approaches.
> 
> > I'm afraid that other hotplug scripts will also have issues with such
> > behavior, and we shouldn't force all users of hotplug scripts to add
> > such workarounds.
> 
> True, iSCSI and other "network" disks might have similar problems.

So I have the following patch which I think might solve your issues
while keeping the reset logic working. Would you mind giving it a try
with your use case and pvgrub?

Thanks, Roger.
---8<---
From c6a76a6265f29440c886b422c9d1b8549ffd6ed8 Mon Sep 17 00:00:00 2001
From: Roger Pau Monne <roger.pau@citrix.com>
Date: Thu, 13 Sep 2018 11:27:57 +0200
Subject: [PATCH] xen-blkback: only set Closed state when resources have been
 released
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Don't set the backend to Closed state until all the resources have
been released and the blkback instance is gone. Setting the backend
state to Closed will be done by xenbus_dev_remove after removing the
device instance.

Note that this requires disconnecting and allowing reconnection with
state Closing, since the Closed state will only be reached when
detaching the device.

Reported-by: Valentin Vidic <Valentin.Vidic@carnet.hr>
Signed-off-by: Roger Pau Monn? <roger.pau@citrix.com>
---
 drivers/block/xen-blkback/xenbus.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index a4bc74e72c39..b0629f1b0511 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -770,7 +770,8 @@ static void frontend_changed(struct xenbus_device *dev,
 
 	switch (frontend_state) {
 	case XenbusStateInitialising:
-		if (dev->state == XenbusStateClosed) {
+		if (dev->state == XenbusStateClosed ||
+		    dev->state == XenbusStateClosing) {
 			pr_info("%s: prepare for reconnect\n", dev->nodename);
 			xenbus_switch_state(dev, XenbusStateInitWait);
 		}
@@ -809,12 +810,12 @@ static void frontend_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateClosing:
+		xen_blkif_disconnect(be->blkif);
 		xenbus_switch_state(dev, XenbusStateClosing);
 		break;
 
 	case XenbusStateClosed:
 		xen_blkif_disconnect(be->blkif);
-		xenbus_switch_state(dev, XenbusStateClosed);
 		if (xenbus_dev_is_online(dev))
 			break;
 		/* fall through */
-- 
2.18.0