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

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Date:	Sun, 27 Sep 2015 20:23:21 -0700
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	yitian <yitian.bu@...gramtek.com>
Cc:	Viresh Kumar <vireshk@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Vinod Koul <vinod.koul@...el.com>, dan.j.williams@...el.com,
	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 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..

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