[Letux-kernel] weird problem with pwm_bl on omap3

Tony Lindgren tony at atomide.com
Thu May 31 01:20:16 CEST 2018

* H. Nikolaus Schaller <hns at goldelico.com> [180529 15:44]:
> I have restarted hunting the issue but it is very
> ghostly. Every time I try to test by another method
> it disappears and if I remove my printk things or
> /etc/modprobe/blacklist.conf it comes back.

Hmm yeah those kind of bugs are annoying :)

> And I tried a bisect but I might not have properly
> detected good/bad and the result points to a commit
> that is very unlikely to make the problem (some patch
> for file system flags).
> Because it seems to depend on the probe/deferred probe
> sequence so it is clearly some race somewhere and I
> am not sure if the pwm_bl is really the source of the
> problem or just happens to do probing at the same moment
> when something else goes wrong.
> I also had another strange effect that sometimes
> only 6 or 7 kernel modules were loaded and shown
> by lsmod. And when I did "modprobe omapdss" it did
> try to load the pwm_bl again several times.
> Now after running several more boot sequences I did
> several times have problems in the generic-adc-battery
> driver and just some minutes ago in the bq27xxx
> driver as well. Both are problems in power_supply_changed_work.
> Every time it is an unexpected NULL pointer dereference
> happening around the moment where pwm_bl is probed.

I guess it could be also some power supply issue?

> At the moment it looks as if *all* such problems occur
> in some worker_thread...
> Next I'll try the CONFIG_DEBUG_SLAB and POISON options.

Yeah that might catch it.



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