On 08/05/2014 03:46 AM, Viresh Kumar wrote: > On 2 August 2014 01:06, Stephen Boyd <sb...@codeaurora.org> wrote: >> I have the same options. The difference is that my driver has a governor >> per policy. That's set with the CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag. > > You may call me stupid but I got a bit confused after looking into the code > again. Why does the crash dump depends on this flag?
Nope, not a stupid question. After reproducing (finally!) yesterday I've been wondering the same thing. > > We *always* remove the governor specific directory while switching governors > (Ofcourse only if its updated for All CPUs). And so on a dual core platform, > where both CPU 0 & 1 share a clock line, switching of governors should result > in this crash dump? I've been looking into *exactly* this. On any platform where cpu_weight(affected_cpus) == 1 for a particular cpu this lockdep trace should happen. > > I may know the answer to the stupid question I had, but not sure why that is a > problem. The only (and quite significant) difference that this flag makes > is the location of governor-specific directory: > - w/o this flag: /sys/devices/system/cpu/cpufreq/<here> > - w/ this flag: /sys/devices/system/cpu/cpu*/cpufreq/<here> > cpufreq_global_kobject vs the policy's kobject. > So, is there some issue with the sysfs lock for <cpu*/cpufreq/> node as while > switching governor we change <cpu*/cpufreq/scaling_governor> at the same > location? That's what I'm wondering too. I'm going to instrument the code to find out this morning. I'm wondering if this comes down to a lockdep class issue (perhaps lockdep puts globally defined locks like cpufreq_global_kobject in a different class?). P. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
