linux-kernel - Re: [PATCH] DMAENGINE: too many kref

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Message-ID: <20071027152816.2d447c70@siona>
Date:	Sat, 27 Oct 2007 15:28:16 +0200
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	Shannon Nelson <shannon.nelson@...el.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	shannon.nelson@...el.com, greg@...ah.com, dan.j.williams@...el.com
Subject: Re: [PATCH] DMAENGINE: too many kref_put calls

On Fri, 26 Oct 2007 16:56:48 -0700
Shannon Nelson <shannon.nelson@...el.com> wrote:

> @@ -134,8 +134,7 @@ static void dma_async_device_cleanup(struct kref
> *kref); 
>  static void dma_dev_release(struct device *dev)
>  {
> -	struct dma_chan *chan = to_dma_chan(dev);
> -	kref_put(&chan->device->refcount, dma_async_device_cleanup);
> +	return;
>  }

Hmm...what prevents dma_chan_cleanup() from being called while someone
still holds a reference to the "class" device? This will allow the
module removal to proceed, the device to be freed, and things will blow
up...

I think my patch is better. By taking two references, the order in
which the cleanup functions are called doesn't matter -- both have to
complete before the module removal is allowed to proceed.

Håvard
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