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

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Date:	Mon, 16 Mar 2009 21:52:10 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Atsushi Nemoto <anemo@....ocn.ne.jp>
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 Mon, Mar 16, 2009 at 7:20 PM, Atsushi Nemoto <anemo@....ocn.ne.jp> wrote:
> On Mon, 16 Mar 2009 14:50:46 -0700, Dan Williams <dan.j.williams@...el.com> wrote:
>> > And above "continue" looks buggy anyway.  Keeping incomplete channels
>> > in device->channels list looks very dangerous...
>>
>> Yes it does.  Here is the proposed fix:
>> ----->
>> dmaengine: fail device registration if channel registration fails
>>
>> From: Dan Williams <dan.j.williams@...el.com>
>>
>> Atsushi points out:
>> "If alloc_percpu or kzalloc failed, chan_id does not match with its
>> position in device->channels list.
>>
>> And above "continue" looks buggy anyway.  Keeping incomplete channels
>> in device->channels list looks very dangerous..."
>>
>> Reported-by: Atsushi Nemoto <anemo@....ocn.ne.jp>
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>
> Thanks, but it seems a hole sill exists.  If alloc_percpu or kzalloc
> for the first channel failed, when idr_ref will be freed ?
>

True, we need a check like the following:

        /* if we never registered a channel just release the idr */
        if (atomic_read(idr_ref) == 0) {
                mutex_lock(&dma_list_mutex);
                idr_remove(&dma_idr, device->dev_id);
                mutex_unlock(&dma_list_mutex);
                kfree(idr_ref);
                return rc;
        }

> Hmm.. why idr_ref is dynamically allocated?  Just putting it in
> dma_device makes thing more simple, no?
>

The sysfs device has a longer lifetime than dma_device.  See commit
41d5e59c [1].

--
Dan

[1] http://git.kernel.org/?p=linux/kernel/git/djbw/async_tx.git;a=commitdiff;h=41d5e59c

> ---
> Atsushi Nemoto
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