On 26 June 2013 23:27, Jacob Shin <jacob.shin@xxxxxxx> wrote: > On Wed, Jun 26, 2013 at 08:02:29PM +0530, Viresh Kumar wrote: >> On 26 June 2013 19:58, Jacob Shin <jacob.shin@xxxxxxx> wrote: >> > On Wed, Jun 26, 2013 at 12:18:27PM +0530, Viresh Kumar wrote: >> >> >> I am not sure if this is enough. What if we had ondemand as the >> >> governor initially, then we changed it to something else. Now also >> >> cur_policy contains a address and isn't zero. > > I just tested this case with this patch applied, and did not have any > problems. Try this: - you need a system with multiple policy groups to test it - Suppose we have two groups of CPUs: 0 and 1 - Set ondemand as governor for both - change governor of group 1 to something else (we still have valid policy struct in Ondemand) - offline all CPUs from group 1. this will free struct cpufreq_policy - Online these CPUs back, this will reallocate policy - Now run this function, the earlier policy struct is already freed and you are accessing it here. >> >> > cpumask_or(&done, &done, policy->cpus); >> >> > + >> >> > + if (policy->governor != &cpufreq_gov_ondemand) >> >> > + continue; >> > >> > This should catch that case no ? >> >> Policy might be freed and reallocated by then. And so doing >> policy->governor is dangerous. > > Are you worried that after we have passed the above if check, and > before we access ->tuner governor change might occur? > > Is there something synonymous to get/put_online_cpus() for cpufreq to > prevent governor change while we update ->tuner values? > > Otherwise, should just spinlock? No, i wasn't worrying about this but a sequence of events that I told to you earlier. Replying to your other mail: > Hm . any hints on how to check for if ondemand is running on this CPU > or not ? I'm not sure what the best way to handle this is .. Make cur_policy zero in cpufreq_governor_dbs() for CPUFREQ_GOV_STOP notification. This will make sure we use correct policy pointer. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
