On Fri, Jun 07, 2013 at 04:39:32PM -0600, Stephen Warren wrote: > On 06/07/2013 04:15 PM, Russell King - ARM Linux wrote: > > For reboot, the real solution there is not to use software-based > > reboot, but bring the other cores to a halt (which is what > > ipi_send_stop is doing) and then issue a hardware reset to the whole > > system, including the other CPUs. > > Ignoring the issues with oops in reboot, I think there's a bug in that > when hotplug is enabled, smp_kill_cpus() calls platform_cpu_kill(), but > nothing causes the failing CPU to ever execute smp_ops.cpu_die(). Hence, > if the implementation of smp_ops.cpu_kill() relies on the target CPU > having run smp_ops.cpu_die(), then smp_ops.cpu_kill() may not operate > correctly. Well, smp_kill_cpus() was added to get around the kexec problem - transitioning from one kernel to the next kernel without going through a hardware reset. Maybe if we take a step back... 1. remove smp_kill_cpus() from smp_send_stop(). 2. remove machine_shutdown() from machine_halt(), machine_power_off() and machine_restart(). 3. call smp_send_stop() only from machine_halt(), machine_power_off() and machine_restart() 4. require a hardware-based reboot method for all SMP implementations; using soft_reboot() is not an option. This should get us into the situation where we have a reliable method of halting and rebooting the kernel everywhere, leaving kexec as being the remaining problem case. Currently, for that we effectively do smp_send_stop() followed by smp_kill_cpus(). The no-op change for kexec there is to allow smp_kill_cpus() to be called directly from machine_shutdown() - but I suspect there will still be stuff that's broken with that... So the ongoing problem remains - how to deal with kexec in a SMP environment where it's difficult to reliably take a secondary CPU offline to a safe place and then be able to restart it into the next kernel... -- 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
