question about alsa tracepoints and alsa debugging

[Bert Schiettecatte]

Hi all,

I have a rk3288 board I am working with, it has two ADCs and one DAC.
The ADCs are connected via an FPGA to the rk3288. The DAC is directly
connected to the I2S port of the rk3288. The rk3288 generates the
master clock. I am using buildroot and busybox and kernel 5.9.12
(stable).

I have a driver which receives the ADC data from the FPGA via SDIO.
When I run speaker-test in the background and use arecord to record
simultaneously in the foreground, both arecord and speaker-test seem
to lock up. When I run speaker-test alone I do not have a problem. The
playback device uses the rockchip_i2s.c driver while the capture
device uses my SDIO driver.

My driver based on dw_mmc.c calls snd_pcm_period_elapsed() for each
buffer of frames that is ready. I can see that this is being called
for a while when I start arecord in the foreground, until the lockup
occurs. The moment I start arecord, the console output from
speaker-test stops, so it's locked up by starting arecord. Previously
this was working fine on kernel 4.11. However, since I updated to
kernel 5.9.12 this no longer works. Has anything changed between 4.11
and 5.9.12 that could be the cause of the problem?

commands used for starting playback / trace capture and for recording -
./perf record -F 99 -g -e snd_pcm:* -e sched:sched_switch -e
sched:sched_wakeup -e irq:* speaker-test -D
hw:CARD=ak4458ak5558aud,DEV=0 -c8 -r192000 -FS32_LE -tsine &
arecord -Dhw:CARD=ak4458ak5558aud,DEV=1 -fS32_LE -c16 -r192000
/mnt/ramdisk/rec.wav

I enabled the kernel options as described at
https://www.kernel.org/doc/html/v5.9/sound/designs/tracepoints.html
and have used perf to record a trace, which can be access here -
https://kernel-debugging.s3-us-west-1.amazonaws.com/perf.data.script.211220202054.txt
(exported using "perf script")

The trace file shows "lockdep_recursion" at some point so I am
wondering if my problem has to do with a deadlock somehow being
caused. However, I also see handle_mm_fault, and do_page_fault, which
has to do with memory mapping? So I'm not sure what the problem
exactly is and what to do next to find out what's wrong.

Thanks in advance for your help and interest and patience,
Bert