linux-kernel - Re: next-20081121:WARNING: at drivers/dma/dmaengine.c:665 dma_async_device

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Date:	Fri, 21 Nov 2008 23:43:59 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: next-20081121:WARNING: at drivers/dma/dmaengine.c:665
 dma_async_device_unregister()

On Fri, 21 Nov 2008 17:53:44 -0700
Dan Williams <dan.j.williams@...el.com> wrote:

> On Fri, 2008-11-21 at 03:40 -0700, Alexander Beregalov wrote:
> > Hi
> > 
> > It occured during shutdown process:
> > 
> > sd 0:2:0:0: [sda] Synchronizing SCSI cache
> > ioatdma 0000:00:08.0: Removing dma and dca services
> > ------------[ cut here ]------------
> > WARNING: at drivers/dma/dmaengine.c:665 dma_async_device_unregister+0x90/0xd0()
> > dma_async_device_unregister called while 1 clients hold a reference
> ...
> > WARNING: at drivers/base/core.c:122 device_release+0x66/0x68()
> > Device 'dma0chan0' does not have a release() function, it is broken and must be
> > fixed.
> 
> The following fixes these up for me.  Maciej, do these look alright?:
> 
> commit 16f5de60e2406c0c879627177aecd7ef489c30e5
> Author: Dan Williams <dan.j.williams@...el.com>
> Date:   Fri Nov 21 17:48:55 2008 -0700
> 
>     dmaengine: add a release for dma class devices
>     
>     Resolves:
>     WARNING: at drivers/base/core.c:122 device_release+0x4d/0x52()
>     Device 'dma0chan0' does not have a release() function, it is broken and must be fixed.
>     
>     Reported-by: Alexander Beregalov <a.beregalov@...il.com>
>     Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 6fc6595..94dcc64 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -103,9 +103,16 @@ static struct device_attribute dma_attrs[] = {
>  	__ATTR_NULL
>  };
>  
> +static void chan_dev_release(struct device *dev)
> +{
> +	/* nothing to do */
> +	do { } while (0);
> +}
> +
>  static struct class dma_devclass = {
>  	.name		= "dma",
>  	.dev_attrs	= dma_attrs,
> +	.dev_release	= chan_dev_release,
>  };

The warning is there for a reason. Device objects can live in sysfs even
after the module is removed. You just wallpapered over the problem..
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