Re: [RFC PATCH] perf/x86/intel/rapl: avoid access unallocate memory
From: Thomas Gleixner
Date: Mon Nov 07 2016 - 11:21:45 EST
On Wed, 2 Nov 2016, Charles (Chas) Williams wrote:
> On 11/02/2016 08:25 AM, Sebastian Andrzej Siewior wrote:
> > I am not sure if this a race with the new hotplug code or something that was
> > always there. Both (M. Vefa Bicakc and Charles) say that the box boots
> > sometimes fine (without the patch). smp_store_boot_cpu_info() should have
> > run
> > before the notofoert and thus should have set the info properly. However I
> > got
> > the following bootlog from Charles with this patch:
> I don't this this is a race. Here is some debugging from the two CPU VM
> (2 sockets, 1 core per socket). In identify_cpu() we have:
> /* The boot/hotplug time assigment got cleared, restore it */
> c->logical_proc_id = topology_phys_to_logical_pkg(c->phys_proc_id);
> The values just after this:
> [ 0.228306] identify_cpu: c ffff88023fd0a040 logical_proc_id 65535
> c->phys_proc_id 2
> So what's interesting here, is the phys_proc_id of 2 for CPU1:
> int topology_phys_to_logical_pkg(unsigned int phys_pkg)
> if (phys_pkg >= max_physical_pkg_id)
> return -1;
> return physical_to_logical_pkg[phys_pkg];
> And we happen to know the max_physical_pkg_id is 2 in this case.
> So apparently, topology_phys_to_logical_pkg() returns -1 and it gets
> assigned to the logical_proc_id.
> I don't know why the CPU's phys_proc_id is 2.
max_physical_pkg_id gets initialized via:
cpus = boot_cpu_data.x86_max_cores;
max_physical_pkg_id = DIV_ROUND_UP(MAX_LOCAL_APIC, ncpus);
What's the value of boot_cpu_data.x86_max_cores and MAX_LOCAL_APIC?