Re: [RFC PATCH] perf/x86/intel/rapl: avoid access unallocate memory

From: Charles (Chas) Williams
Date: Wed Nov 02 2016 - 18:48:21 EST

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.