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

From: Andy Shevchenko
Date: Mon Sep 28 2015 - 03:05:49 EST

On Mon, Sep 28, 2015 at 6:23 AM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> On 26 September 2015 at 05:38, yitian <yitian.bu@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
>> ---
>> 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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