Re: [PATCH] perf/x86/intel/rapl: Rename rapl_cpu_prepare() to rapl_cpu_starting()

[Yasuaki Ishimatsu]

Hi Thomas,

Do you have any idea to fix the issue?
If you have the idea, please send me the patch.

Thanks,
Yasuaki Ishimatsu

On 01/24/2017 02:54 PM, Thomas Gleixner wrote:
> On Tue, 24 Jan 2017, Yasuaki Ishimatsu wrote:
> > rapl_cpu_prepare() must be called after logical package id of CPU
> > is set by topology_update_package_map().
> >
> > But when onlining hot-added CPU, rapl_cpu_prepare() is called before
> > setting logical package id of the hot-added CPU. So cpu_to_rapl_pmu()
> > in rapl_cpu_prepare() finds a rapl_pmu of wrong logical package id and
> > rapl_cpu_prepare() initializes the wrong rapl_pmu.
> >
> > After that logical package id of the hot-added CPU is set by
> > topology_update_package_map(). But rapl_cpu_prepare() does
> > not initialize pmu of the logical package id of the hot-added CPU.
> > So when calling rapl_cpu_online(), cpu_to_rapl_pmu() returns NULL and
> > the following NULL pointer dereference occurs.
> >
> >   BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> >   IP: rapl_cpu_online+0x8d/0xb0
> >   <snip>
> >   Call Trace:
> >    ? rapl_cpu_offline+0xc0/0xc0
> >    cpuhp_invoke_callback+0x8d/0x3f0
> >    cpuhp_up_callbacks+0x37/0xb0
> >    cpuhp_thread_fun+0xc9/0xe0
> >    smpboot_thread_fn+0x110/0x160
> >    kthread+0x101/0x140
> >    ? sort_range+0x30/0x30
> >    ? kthread_park+0x90/0x90
> >    ret_from_fork+0x25/0x30
> >
> > The patch renames rapl_cpu_prepare() to rapl_cpu_starting() and changes
> > the position of cpuhp_state so that rapl_cpu_starting() is called
> > after topology_update_package_map().
>
> Does not work. You cannot call that callback in the starting context. It
> does allocations. This needs be fixed in a different way. I'll have a look
> tomorrow.
>
> Thanks,
>
> 	tglx