linux-kernel - Re: [PATCH] perf/x86/intel/rapl: Rename rapl_cpu_prepare() to rapl_cpu

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Date:   Mon, 30 Jan 2017 11:36:53 -0500
From:   Yasuaki Ishimatsu <yasu.isimatu@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] perf/x86/intel/rapl: Rename rapl_cpu_prepare() to
 rapl_cpu_starting()

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
>