linux-kernel - Re: [PATCH v2] soc: qcom: pdr: Fix the potential deadlock

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Message-ID: <Z6x_GJg92ddzoRwQ@hovoldconsulting.com>
Date: Wed, 12 Feb 2025 11:59:36 +0100
From: Johan Hovold <johan@...nel.org>
To: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>, konradybcio@...nel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Saranya R <quic_sarar@...cinc.com>,
	Frank Oltmanns <frank@...manns.dev>
Subject: Re: [PATCH v2] soc: qcom: pdr: Fix the potential deadlock

On Wed, Feb 12, 2025 at 10:37:35AM +0100, Johan Hovold wrote:
> On Tue, Feb 11, 2025 at 10:37:11PM +0530, Mukesh Ojha wrote:
> > On Mon, Feb 10, 2025 at 10:43:23AM +0100, Johan Hovold wrote:

> > > A Link tag to my report would be good to have as well if this fixes the
> > > audio regression.
> > 
> > I see this is somehow matching the logs you have reported, but this deadlock
> > is there from the very first day of pdr_interface driver.
> > 
> > [   14.565059] PDR: avs/audio get domain list txn wait failed: -110
> > [   14.571943] PDR: service lookup for avs/audio failed: -110
> 
> Yes, but using the in-kernel pd-mapper has exposed a number of existing
> bugs since it changes the timing of events enough to make it easier to
> hit them.
> 
> The audio regression is a very real regression for users of Snapdragon
> based laptops like, for example, the Lenovo Yoga Slim 7x.
> 
> If Bjorn has confirmed that this is the same issue (I can try to
> instrument the code based on your analysis to confirm this too), then I
> think it would be good to mention this in the commit message and link to
> the report, for example:
> 
> 	This specifically also fixes an audio regression when using the
> 	in-kernel pd-mapper as that makes it easier to hit this race. [1]
> 
> 	Link: https://lore.kernel.org/lkml/Zqet8iInnDhnxkT9@hovoldconsulting.com/ # [1]
> 
> or similar.

I can confirm that audio regression with the in-kernel pd-mapper appears
to be caused by the race that this patch fixes.

If I insert a short (100-200 ms) sleep before taking the list lock in
pdr_locator_new_server() to increase the race window, I see the audio
service failing to register on both the X1E CRD and Lenovo ThinkPad
X13s:

[   11.118557] pdr_add_lookup - tms/servreg / msm/adsp/charger_pd
[   11.443632] pdr_locator_new_server
[   11.558122] pdr_locator_new_server - taking list lock
[   11.563939] pdr_locator_new_server - releasing list lock
[   11.582178] pdr_locator_work - taking list lock
[   11.594468] pdr_locator_work - releasing list lock
[   11.992018] pdr_add_lookup - avs/audio / msm/adsp/audio_pd
[   11.992034] pdr_add_lookup - avs/audio / msm/adsp/audio_pd
[   11.992224] pdr_locator_new_server
    < 100 ms sleep inserted before taking lock in pdr_locator_new_server() >
[   11.997937] pdr_locator_work - taking list lock
[   12.093984] pdr_locator_new_server - taking list lock
[   17.120169] PDR: avs/audio get domain list txn wait failed: -110
[   17.127066] PDR: service lookup for avs/audio failed: -110
[   17.132893] pdr_locator_work - releasing list lock
[   17.139885] pdr_locator_new_server - releasing list lock

[ On the X13s, where I have not hit this issue with the in-kernel
  pd-mapper, I had to make sure to insert the sleep only on the second
  call, possibly because of interaction with the charger_pd registration
  which happened closer to the audio registration. ]

Please add a comment and link to the audio regression report as I
suggested above, and feel free to include my:

	Tested-by: Johan Hovold <johan+linaro@...nel.org>

Thanks for fixing this!

Johan