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Date:   Fri, 7 Sep 2018 12:20:26 +0200
From:   Valentin Vidic <Valentin.Vidic@CARNet.hr>
To:     Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Jens Axboe <axboe@kernel.dk>, xen-devel@lists.xenproject.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, drbd-user@lists.linbit.com
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User-Agent: Mutt/1.10.1 (2018-07-13)
Subject: Re: [PATCH] xen-blkback: Switch to closed state after releasing the
 backing device
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Sep 07, 2018 at 09:54:55AM +0200, Roger Pau Monn? wrote:
> Then I'm afraid you will have to look into the vbd_free/create fix.

Yes, here is a first draft for that idea, let me know if you see some
problems there:

--- xenbus.c.orig       2018-09-07 12:11:57.798071485 +0200
+++ xenbus.c    2018-09-07 12:14:23.536077992 +0200
@@ -758,6 +759,7 @@
                             enum xenbus_state frontend_state)
 {
        struct backend_info *be = dev_get_drvdata(&dev->dev);
+       struct block_device *bdev;
        int err;
 
        pr_debug("%s %p %s\n", __func__, dev, xenbus_strstate(frontend_state));
@@ -772,6 +774,22 @@
 
        case XenbusStateInitialised:
        case XenbusStateConnected:
+               if (!be->blkif->vbd.bdev) {
+                       printk("blkdev_get");
+                       bdev = blkdev_get_by_dev(be->blkif->vbd.pdevice,
+                                                be->blkif->vbd.readonly ?
+                                                FMODE_READ : FMODE_WRITE, NULL);
+
+                       if (IS_ERR(bdev)) {
+                               pr_warn("frontend_changed: device %08x could not be opened\n",
+                                       be->blkif->vbd.pdevice);
+                               break;
+                       }
+
+                       printk("blkdev_get good");
+                       be->blkif->vbd.bdev = bdev;
+               }
+
                /*
                 * Ensure we connect even when two watches fire in
                 * close succession and we miss the intermediate value
@@ -808,6 +826,7 @@
 
        case XenbusStateClosed:
                xen_blkif_disconnect(be->blkif);
+               xen_vbd_free(&be->blkif->vbd);
                xenbus_switch_state(dev, XenbusStateClosed);
                if (xenbus_dev_is_online(dev))
                        break;

-- 
Valentin