linux-kernel - [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when detaching device

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Date:   Tue, 4 Jul 2017 13:48:32 +0200
From:   Vincent Legout <vincent.legout@...di.net>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Roger Pau Monné <roger.pau@...rix.com>,
        xen-devel@...ts.xenproject.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when detaching device

Devices are not unmounted inside a domU after a xl block-detach.

After xl block-detach, blkfront_closing() is called with state ==
XenbusStateConnected, it detects that the device is still in use and
only switches state to XenbusStateClosing. blkfront_closing() is called
a second time but returns immediately because state ==
XenbusStateClosing. Thus the device keeps being mounted inside the domU.

To fix this, emit a KOBJ_OFFLINE uevent even if the device has users.

With this patch, inside domU, udev has:

KERNEL[16994.526789] offline  /devices/vbd-51728/block/xvdb (block)
KERNEL[16994.796197] remove   /devices/virtual/bdi/202:16 (bdi)
KERNEL[16994.797167] remove   /devices/vbd-51728/block/xvdb (block)
UDEV  [16994.798035] remove   /devices/virtual/bdi/202:16 (bdi)
UDEV  [16994.809429] offline  /devices/vbd-51728/block/xvdb (block)
UDEV  [16994.842365] remove   /devices/vbd-51728/block/xvdb (block)
KERNEL[16995.461991] remove   /devices/vbd-51728 (xen)
UDEV  [16995.462549] remove   /devices/vbd-51728 (xen)

While without, it had:

KERNEL[30.862764] remove   /devices/vbd-51728 (xen)
UDEV  [30.867838] remove   /devices/vbd-51728 (xen)

Signed-off-by: Pascal Bouchareine <pascal@...di.net>
Signed-off-by: Fatih Acar <fatih.acar@...di.net>
Signed-off-by: Vincent Legout <vincent.legout@...di.net>
---
 drivers/block/xen-blkfront.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 39459631667c..da0b0444ee1f 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -2185,8 +2185,10 @@ static void blkfront_closing(struct blkfront_info *info)
 	mutex_lock(&bdev->bd_mutex);
 
 	if (bdev->bd_openers) {
-		xenbus_dev_error(xbdev, -EBUSY,
-				 "Device in use; refusing to close");
+		dev_warn(disk_to_dev(info->gd),
+			 "detaching %s with pending users\n",
+			 xbdev->nodename);
+		kobject_uevent(&disk_to_dev(info->gd)->kobj, KOBJ_OFFLINE);
 		xenbus_switch_state(xbdev, XenbusStateClosing);
 	} else {
 		xlvbd_release_gendisk(info);
-- 
2.13.2