linux-kernel - Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver

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Date:	Wed, 18 Mar 2009 09:49:35 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	dan.j.williams@...el.com
Cc:	linux-mips@...ux-mips.org, ralf@...ux-mips.org,
	linux-kernel@...r.kernel.org, haavard.skinnemoen@...el.com
Subject: Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver

On Tue, 17 Mar 2009 10:02:14 -0700, Dan Williams <dan.j.williams@...el.com> wrote:
> >> The sysfs device has a longer lifetime than dma_device.  See commit
> >> 41d5e59c [1].
> >
> > The sysfs device for dma_chan (dma_chan_dev) has a shorter lifetime
> > than dma_device, doesn't it?
> 
> No,  dma_async_device_unregister(), and the freeing of dma_device, may
> finish before chan_dev_release is called.  Userspace gates the final
> release of dma_chan_dev objects.

You mean, if the sysfs device file was opened when
dma_async_device_unregister() was called, the sysfs device will not be
released until the sysfs device file is closed, right?  If so I can
see.

BTW, there are another holes in dma_async_device_register.  If
idr_pre_get or idr_get_new was failed, idr_ref will not be freed.

---
Atsushi Nemoto
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