On Sun, Dec 23, 2012 at 11:25:40AM +0000, Will Deacon wrote: > On Fri, Dec 21, 2012 at 09:23:17PM +0000, Stephen Warren wrote: > > What exactly did you mean by "what we currently have"; did you mean that > > cpu_kill() should work without cpu_die() having executed on the target > > CPU itself first, so Tegra should simply implement cpu_kill()? As Joseph > > says above, I'm not sure that will work. Any more detailed thoughts you > > have here would be greatly appreciated. Thanks. > > I guess this comes down to the different between cpu_die/cpu_kill and > whether you actually need cpu_die if you're not planning on returning to > the same kernel that you left. If you really need to call cpu_die, then we > need to figure out a way to do that whilst ensuring that only one CPU is > left standing at the time we start copying the new kernel into place. I took a closer look at the code to try and figure out a way to solve this... First of all, disable_nonboot_cpus *does* actually wait for the secondaries to get out of the way, because it calls __cpu_die and we end up waiting on a completion. The problem is that we IPI the secondaries in smp_send_stop, which puts then into a while(1) cpu_relax(); loop with interrupts disabled, so that completion won't be able to finish (the cores won't pass through idle and call cpu_die() themselves). This means we must call disable_nonboot_cpus before sending the IPI. My first attempt was to make a hotplug-aware smp_send_stop, using disable_nonboot_cpus and smp_kill_cpus but this is also problematic because it's called by panic, where the simpler IPI-based code is probably a lot better. The best bet is probably to call disable_nonboot_cpus in machine shutdown, before sending the stop and subsequent kill. It's very similar to your initial suggestion, but without the #elif. Does that work for you? Will -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
