Re: [BUG] While changing the cpufreq governor, kernel hits a bug in workqueue.c

[Johannes Weiner <hannes@saeurebad.de>]

Hi Nageswara,

Nageswara R Sastry <rnsastry@linux.vnet.ibm.com> writes:

> Any updates on this bug.

Sorry.  I was just looking into it again and still see no resolution.
Added Venkatesh and Alexey to CC.

To summarize again:

The problem we have is that cpufreq_ondemand has a self-rearming worker
function which we should but can not cancel synchroneously with the
current code.  The locking order is like this:

store()
  policy_rwsem write
    cpufreq_governor_dbs()
    dbs_mutex

work lock
  do_dbs_timer()
    policy_rwsem write

which gives a locking hierarchy of:

work lock
  policy_rwsem
    dbs_mutex

Now, we _should_ cancel the worker synchroneously, but that won't fly
since when cpufreq_governor_dbs() is called, we already hold
policy_rwsem and grabbing the work lock is illegal.

I will continue to read code and see if I can come up with a solution,
but any help is really appreciated.

I have not yet looked at cpufreq_conservative...

> Thanks and Regards
> R.Nageswara Sastry

Thanks for your patience and insistence,

	Hannes