[yocto] (IIO) ADC freeze on am335x processor on 3.14.26ltsi kernel

[Yani Dubin]

Hi,

I have run up against a kernel bug on the dizzy branch where a read of an
ADC channel (IIO bus) on a Sitara (am335x) processor locks up the process
reading the /sys/bus/iio/devices/iio\:device0/in_voltage?_raw node. The
system remains stable, but the locked process does not respond to SIGKILL.
No kernel errors or debugging info in the logs - but I have taken no steps
to improve verbosity. fuser shows the files as being open by the crashed
process.

I did google the issue, but turned up nothing. This is very reproduceable,
and I have done my best to narrow it down on the dizzy timeline. In each
case I have used the same rootfs (built from dizzy tip), but just flashed a
different kernel.

The (yocto) changesets in question are:
36e42c0ddb7a40b3022e9b165560622479f1aa5c  - 3.14.26ltsi exhibits issue
446acfb5a474b23041b46c49732474f2d415160d   - 3.14.24 doesn't build
d7c61053da96d675c3912a45ee448c20ae91721b - 3.14.19 issue not present

The build error in question is "ERROR: Fetcher failure: Unable to find
revision fba2d0cdb745e0f807ce134fd9d1524b7bed9742 in branch meta even from
upstream".

These are 3 adjacent changesets on the dizzy branch - I gather that is as
much as I can narrow it down?

Should I be submitting this bug to yocto bugzilla (since it affects the
stable release, and I am using linux-yocto) or a linux kernel bug tracker /
mailing list? Or is there further information I should be getting (enabling
kernel debugging / increasing verbosity perhaps)? Should I do a build off
the unstable branch for comparison? (to see if this has a newer kernel,
with upstream fix which resolves the issue)

Meanwhile, I thought I would see if anyone else is experiencing this, or
has similar hardware and can see if they are also affected. This is a
custom board, but similar processor-wise to the Beaglebone Black.

Steps to reproduce:
cat /sys/bus/iio/devices/iio\:device0/in_voltage?_raw

The particular drivers in use are:
CONFIG_TI_AM335X_ADC=y
CONFIG_MFD_TI_AM335X_TSCADC=y

Regards,
Yani.

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