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

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Date:   Tue, 4 Jul 2017 17:59:27 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Vincent Legout <vincent.legout@...di.net>
CC:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when detaching
 device

On Tue, Jul 04, 2017 at 01:48:32PM +0200, Vincent Legout wrote:
> 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)

I'm not an expect on udev, but aren't those messages duplicated? You
seem to get one message from udev and another one from the kernel.

> 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);

What happens if you simply remove the xenbus_dev_error but don't add
the kobject_uevent?

I'm asking because I don't see any other block device calling
directly kobject_uevent, and I'm sure this should be pretty similar to
what virtio or USB do when a block device is hot-unplugged.

For example blk_unregister_queue already contains a call to trigger a
kobject_uevent.

Thanks, Roger.