linux-kernel - Re: [PATCH] Xen: Fix warning when hot-unplugging virtual block devices

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Date:	Thu, 21 Aug 2008 13:13:08 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Alex Nixon <alex.nixon@...rix.com>
CC:	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH] Xen: Fix warning when hot-unplugging virtual block devices

Alex Nixon wrote:
> From: Alex Nixon <alex.nixon@...rix.com>
> Date: Thu, 21 Aug 2008 12:30:54 +0100
> Subject: [PATCH] Xen: Fix warning when hot-unplugging virtual block devices
>
> WARNING: at kernel/softirq.c:136 local_bh_enable+0x3f/0x8a()
>
> del_gendisk needs IRQs enabled, as the code path eventually reaches local_bh_enable.
> blk_stop_queue needs them disabled - so do so temporarily.
>
> It shouldn't matter if an interrupt comes in whilst blkif_io_lock is held, as it will block on the lock.  Upon acquisition, it'll realise the device is down and exit cleanly.
>
> Signed-off-by: Alex Nixon <alex.nixon@...rix.com>
>   
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

Send a clean copy to Jens with my ack.

    J
> ---
>  drivers/block/xen-blkfront.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index d5e7532..95cee2c 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -899,16 +899,18 @@ static void blkfront_closing(struct xenbus_device *dev)
>  	if (info->rq == NULL)
>  		goto out;
>  
> -	spin_lock_irqsave(&blkif_io_lock, flags);
> +	spin_lock(&blkif_io_lock);
>  
>  	del_gendisk(info->gd);
>  
> +	local_irq_save(flags);
>  	/* No more blkif_request(). */
>  	blk_stop_queue(info->rq);
> +	local_irq_restore(flags);
>  
>  	/* No more gnttab callback work. */
>  	gnttab_cancel_free_callback(&info->callback);
> -	spin_unlock_irqrestore(&blkif_io_lock, flags);
> +	spin_unlock(&blkif_io_lock);
>  
>  	/* Flush gnttab callback work. Must be done with no locks held. */
>  	flush_scheduled_work();
>   

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