On Tuesday, February 25, 2014 02:20:57 PM Viresh Kumar wrote: > On 25 February 2014 01:53, Saravana Kannan <skannan@xxxxxxxxxxxxxx> wrote: > > I was simplifying the scenario that causes it. We change the min/max using > > ADJUST notifiers for multiple reasons -- thermal being one of them. > > > > thermal/cpu_cooling is one example of it. > > Just to understand the clear picture, you are actually hitting this bug? Or > is this only a theoretical bug? > > > So, cpufreq_update_policy() can be called on any CPU. If that races with > > someone offlining a CPU and onlining it, you'll get this crash. > > Then shouldn't that be fixed by locks? I think yes. That makes me agree with > Srivatsa more here. > > Though I would say that your argument was also valid that 'policy' shouldn't be > up for sale unless it is prepared to. And for that reason only I > floated that question > earlier: What exactly we need to make sure is initialized in policy? Because > policy might keep changing in future as well and that needs locks to protect > that stuff. Like min/max/governor/ etc.. Well, that depends on what the current users expect it to look like initially. It should be initialized to the point in which all of them can handle it correctly. > So, probably a solution here might be a mix of both. Initialize policy to this > minimum level and then make sure locking is used correctly.. Yes. > > The idea would exist, but we can just call cpufreq_generic_get() and pass it > > policy->clk if it is not NULL. Does that work for you? > > No. Not all drivers implement clk interface. And so clk doesn't look to be the > right parameter. I thought maybe 'policy' can be the right parameter and > then people can get use policy->cpu to get cpu id out of it. > > But even that doesn't look to be a great idea. X86 drivers may share policy > structure for CPUs that don't actually share a clock line. And so they do need > right CPU number as parameter instead of policy. As they might be doing > some tricky stuff there. Also, we need to make sure that ->get() returns > the frequency at which CPU x is running. That's not going to work in at least some cases anyway, because for some types of HW we simply can't retrieve the current frequency in a non-racy way. Thanks! -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
