From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH] xen/blkfront: fix warning when deleting
	gendisk on unplug/shutdown.
Date: Mon, 18 May 2009 12:11:01 -0700
Message-ID: <4A11B2C5.1020205@goop.org>
References: <1242650931.20731.41.camel@zakaz.uk.xensource.com>
	<1242650974-13056-1-git-send-email-ian.campbell@citrix.com>
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To: Ian Campbell <ian.campbell@citrix.com>
Cc: xen-devel@lists.xensource.com, Jens Axboe <jens.axboe@oracle.com>
List-Id: xen-devel@lists.xenproject.org

Ian Campbell wrote:
> Currently blkfront gives a warning when hot unplugging due to calling
> del_gendisk() with interrupts disabled (due to blkif_io_lock).
>
> WARNING: at kernel/softirq.c:124 local_bh_enable+0x36/0x84()
> Modules linked in: xenfs xen_netfront ext3 jbd mbcache xen_blkfront
> Pid: 13, comm: xenwatch Not tainted 2.6.29-xs5.5.0.13 #3
> Call Trace:
>  [<c012611c>] warn_slowpath+0x80/0xb6
>  [<c0104cf1>] xen_sched_clock+0x16/0x63
>  [<c0104710>] xen_force_evtchn_callback+0xc/0x10
>  [<c0104e32>] check_events+0x8/0xe
>  [<c0104d9b>] xen_restore_fl_direct_end+0x0/0x1
>  [<c0103749>] xen_mc_flush+0x10a/0x13f
>  [<c0105bd2>] __switch_to+0x114/0x14e
>  [<c011d92b>] dequeue_task+0x62/0x70
>  [<c0123b6f>] finish_task_switch+0x2b/0x84
>  [<c0299877>] schedule+0x66d/0x6e7
>  [<c0104710>] xen_force_evtchn_callback+0xc/0x10
>  [<c0104710>] xen_force_evtchn_callback+0xc/0x10
>  [<c012a642>] local_bh_enable+0x36/0x84
>  [<c022f9a7>] sk_filter+0x57/0x5c
>  [<c0233dae>] netlink_broadcast+0x1d5/0x315
>  [<c01c6371>] kobject_uevent_env+0x28d/0x331
>  [<c01e7ead>] device_del+0x10f/0x120
>  [<c01e7ec6>] device_unregister+0x8/0x10
>  [<c015f86d>] bdi_unregister+0x2d/0x39
>  [<c01bf6f4>] unlink_gendisk+0x23/0x3e
>  [<c01ac946>] del_gendisk+0x7b/0xe7
>  [<d0828c19>] blkfront_closing+0x28/0x6e [xen_blkfront]
>  [<d082900c>] backend_changed+0x3ad/0x41d [xen_blkfront]
>
> We can fix this by calling del_gendisk() later in blkfront_closing, after
> releasing blkif_io_lock. Since the queue is stopped during the interrupts
> disabled phase I don't think there is any danger of an event occuring between
> releasing the blkif_io_lock and deleting the disk.
>
> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
>   

Looks OK to me.  Alex Nixon came up with more or less the same patch to 
replace his first failed attempt to fix this.  It looks much better than 
mucking around with interrupts states.

Jens?  How does it look to you?

Thanks,
    J

> ---
>  drivers/block/xen-blkfront.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 8f90508..aa0c94b 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -934,8 +934,6 @@ static void blkfront_closing(struct xenbus_device *dev)
>  
>  	spin_lock_irqsave(&blkif_io_lock, flags);
>  
> -	del_gendisk(info->gd);
> -
>  	/* No more blkif_request(). */
>  	blk_stop_queue(info->rq);
>  
> @@ -949,6 +947,8 @@ static void blkfront_closing(struct xenbus_device *dev)
>  	blk_cleanup_queue(info->rq);
>  	info->rq = NULL;
>  
> +	del_gendisk(info->gd);
> +
>   out:
>  	xenbus_frontend_closed(dev);
>  }
>