linux-kernel - Re: [PATCH 1/1] dmaengine: dw: resolve recursion lock when audio playback

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Date:	Mon, 28 Sep 2015 10:05:43 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	yitian <yitian.bu@...gramtek.com>,
	Viresh Kumar <vireshk@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	dmaengine <dmaengine@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] dmaengine: dw: resolve recursion lock when audio playback

On Mon, Sep 28, 2015 at 6:23 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 26 September 2015 at 05:38, yitian <yitian.bu@...gramtek.com> wrote:
>> when audio playback is running, user space will call
>> snd_pcm_lib_write1() function, it will first get pcm stream lock,
>> after that it may call function snd_pcm_update_hw_ptr(), the call
>> stack will be as below:
>>   snd_pcm_lib_write1  <-- got pcm stream lock
>>    --> snd_pcm_update_hw_ptr
>>      --> dwc_tx_status
>>       --> dwc_scan_descriptors
>>        --> callback
>>         --> dmaengine_pcm_dma_complete
>>          --> snd_pcm_period_elapsed <-- get stream lock again
>> recursion lock occurs in snd_pcm_period_elapsed function.
>> remove dwc_scan_descriptors from dwc_tx_status can fix this issue.
>>
>> Signed-off-by: Yitian Bu <yitian.bu@...gramtek.com>
>> ---
>>  drivers/dma/dw/core.c | 6 +-----
>>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> I am not sure if this is a sane way of doing that, and we were scanning
> the descriptors for some valid reason..

Actually one of the patches in a pile sitting in my private repo is
also including similar change. In my case the reason is to support
cyclic transfers natively.

> Though, I am on vacation for few days now and will be able to look
> at the details later.

Have a good rest then!

-- 
With Best Regards,
Andy Shevchenko
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