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

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

[Alex Nixon]

From: Alex Nixon <alex.nixon@citrix.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@citrix.com>
---
 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();
-- 
1.5.4.3

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

[Jeremy Fitzhardinge]

Alex Nixon wrote:
> From: Alex Nixon <alex.nixon@citrix.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@citrix.com>
>   
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.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();
>