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

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Message-ID: <alpine.DEB.2.20.1611071717000.3709@nanos>
Date:   Mon, 7 Nov 2016 17:19:04 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Charles (Chas) Williams" <ciwillia@...cade.com>
cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "M. Vefa Bicakci" <m.v.b@...box.com>
Subject: Re: [RFC PATCH] perf/x86/intel/rapl: avoid access unallocate
 memory

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?

Thanks,

	tglx