Re: [lkp] [sched/fair] 41e0d37f7a: divide error: 0000 [#1] SMP

[Wanpeng Li]

2016-05-03 23:10 GMT+08:00 Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>:
> On Tuesday, May 03, 2016 03:53:12 PM Rafael J. Wysocki wrote:
>> On Tuesday, May 03, 2016 03:22:24 PM Rafael J. Wysocki wrote:
>> > On Tue, May 3, 2016 at 2:58 PM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>> > > On Tue, May 3, 2016 at 2:54 PM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>> > >> On Tue, May 3, 2016 at 2:15 PM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>> > >>> On Tue, May 3, 2016 at 10:32 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> > >>>> On Tue, May 03, 2016 at 09:10:51AM +0800, kernel test robot wrote:
>> > >>>>> FYI, we noticed the following commit:
>> > >>>>>
>> > >>>>> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core
>> > >>>>> commit 41e0d37f7ac81297c07ba311e4ad39465b8c8295 ("sched/fair: Do not call cpufreq hook unless util changed")
>> > >>>>
>> > >>>>
>> > >>>>> [   14.860950] Freeing unused kernel memory: 260K (ffff88103edbf000 - ffff88103ee00000)
>> > >>>>> [   14.873013] systemd[1]: RTC configured in localtime, applying delta of 480 minutes to system time.
>> > >>>>> [   14.884474] random: systemd urandom read with 5 bits of entropy available
>> > >>>>> [   14.903975] divide error: 0000 [#1] SMP
>> > >>>>> [   14.908375] Modules linked in:
>> > >>>>> [   14.911793] CPU: 39 PID: 1 Comm: systemd Not tainted 4.6.0-rc4-00016-g41e0d37 #1
>> > >>>>> [   14.920051] Hardware name: Intel Corporation S2600WP/S2600WP, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013
>> > >>>>> [   14.931509] task: ffff8810101d8000 ti: ffff88081ab20000 task.ti: ffff88081ab20000
>> > >>>>> [   14.939862] RIP: 0010:[<ffffffff8176ad32>]  [<ffffffff8176ad32>] intel_pstate_get+0x32/0x40
>> > >>>>> [   14.949202] RSP: 0018:ffff88081ab23d70  EFLAGS: 00010006
>> > >>>>> [   14.955129] RAX: 0000000000000000 RBX: 0000000000000024 RCX: ffff8808091e0300
>> > >>>>> [   14.963094] RDX: 0000000000000000 RSI: 0000000000000100 RDI: 0000000000000024
>> > >>>>> [   14.971057] RBP: ffff88081ab23d88 R08: 0000000000001000 R09: 00000000096a1000
>> > >>>>> [   14.979022] R10: 0000000000ffff10 R11: 000000000000000f R12: 0000000000000202
>> > >>>>> [   14.986984] R13: ffff88101390a040 R14: ffff88100e48e180 R15: ffff88101390a040
>> > >>>>> [   14.994950] FS:  00007f66fe117880(0000) GS:ffff8810139c0000(0000) knlGS:0000000000000000
>> > >>>>> [   15.003982] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> > >>>>> [   15.010393] CR2: 000055f78b760098 CR3: 000000103d759000 CR4: 00000000001406e0
>> > >>>>> [   15.018359] Stack:
>> > >>>>> [   15.020602]  ffffffff81764dad 0000000000000024 ffff88100e48e180 ffff88081ab23dc8
>> > >>>>> [   15.028899]  ffffffff81040267 ffff88101390a0ac 0000000000000340 ffff88081ab23f20
>> > >>>>> [   15.037197]  ffff88103cd7c400 ffff88100e48e180 ffff88101390a040 ffff88081ab23e30
>> > >>>>> [   15.045493] Call Trace:
>> > >>>>> [   15.048223]  [<ffffffff81764dad>] ? cpufreq_quick_get+0x3d/0x90
>> > >>>>> [   15.054832]  [<ffffffff81040267>] show_cpuinfo+0x3c7/0x410
>> > >>>>> [   15.060956]  [<ffffffff8121f5c4>] seq_read+0x2c4/0x3a0
>> > >>>>> [   15.066685]  [<ffffffff81266ea8>] proc_reg_read+0x48/0x70
>> > >>>>> [   15.072713]  [<ffffffff811f9d58>] __vfs_read+0x28/0xd0
>> > >>>>> [   15.078451]  [<ffffffff813bab63>] ? security_file_permission+0xa3/0xc0
>> > >>>>> [   15.085737]  [<ffffffff811faa97>] ? rw_verify_area+0x57/0xd0
>> > >>>>> [   15.092054]  [<ffffffff811fab96>] vfs_read+0x86/0x130
>> > >>>>> [   15.097691]  [<ffffffff811fbf96>] SyS_read+0x46/0xa0
>> > >>>>> [   15.103234]  [<ffffffff818f71b2>] entry_SYSCALL_64_fastpath+0x1a/0xa4
>> > >>>>> [   15.110421] Code: 05 dc 1b c3 00 89 ff 55 48 89 e5 48 8b 0c f8 48 85 c9 74 1f 48 63 51 1c 48 63 41 20 5d 48 0f af c2 31 d2 48 0f af 81 88 00 00 00 <48> f7 b1 90 00 00 00 c3 31 c0 5d c3 66 90 0f 1f 44 00 00 8b 77
>> > >>>>> [   15.132161] RIP  [<ffffffff8176ad32>] intel_pstate_get+0x32/0x40
>> > >>>>> [   15.138875]  RSP <ffff88081ab23d70>
>> > >>>>> [   15.142770] ---[ end trace e5d5a8bedf5502e1 ]---
>> > >>>>> [   15.149323] Kernel panic - not syncing: Fatal exception
>> > >>>>>
>> > >>>>
>> > >>>> That's intel_pstate.c:get_avg_frequency(), which assumes mperf != 0. It
>> > >>>> being 0 seems to suggest intel_pstate_sample() hasn't been called yet or
>> > >>>> so.
>> > >>>
>> > >>> Well, what's the tree based on?
>> > >>>
>> > >>> The mainline does this:
>> > >>>
>> > >>> bool sample_taken = intel_pstate_sample(cpu, time);
>> > >>>
>> > >>> if (sample_taken && !hwp_active)
>> > >>>         intel_pstate_adjust_busy_pstate(cpu);
>> > >>>
>> > >>> and (the mainline version of) intel_pstate_sample() returns false when
>> > >>> it is called for the first time after setting the update_util hook.
>> > >>
>> > >> If that helps, I can expose my pm-cpufreq-fixes branch to pull from.
>> > >> It contains all cpufreq material that went into the Linus' tree to
>> > >> date and is based on 4.5-rc3.
>> > >
>> > > In fact, it is exposed already:
>> > >
>> > > git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git \
>> > > pm-cpufreq-fixes
>> > >
>> > > and the top-most commit is 1becf03545a0859ceaaf9e8c2d9861882a71cb01
>> > > (cpufreq: intel_pstate: Fix processing for turbo activation ratio).
>> >
>> > Ah, that will fail as well.
>> >
>> > The problem is that intel_pstate_get() can be called before we take
>> > the first sample.
>> >
>> > I need to think about how to fix that.
>>
>> Maybe something like the below (untested, but builds).
>>
>> It will make intel_pstate_get() return 0 until avg_frequency gets populated
>> which is actually OK.
>
> The previous one would break the HWP case, so below is a new one (still
> untested).

I can reproduce the bug and your patch fix it.

Tested-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

>
> ---
>  drivers/cpufreq/intel_pstate.c |   19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
>
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -114,6 +114,7 @@ struct cpudata {
>         u64     prev_mperf;
>         u64     prev_tsc;
>         u64     prev_cummulative_iowait;
> +       int     avg_frequency;
>         struct sample sample;
>  };
>
> @@ -1044,7 +1045,7 @@ static inline void intel_pstate_adjust_b
>                 sample->mperf,
>                 sample->aperf,
>                 sample->tsc,
> -               get_avg_frequency(cpu));
> +               cpu->avg_frequency);
>  }
>
>  static void intel_pstate_update_util(struct update_util_data *data, u64 time,
> @@ -1056,8 +1057,11 @@ static void intel_pstate_update_util(str
>         if ((s64)delta_ns >= pid_params.sample_rate_ns) {
>                 bool sample_taken = intel_pstate_sample(cpu, time);
>
> -               if (sample_taken && !hwp_active)
> -                       intel_pstate_adjust_busy_pstate(cpu);
> +               if (sample_taken) {
> +                       cpu->avg_frequency = get_avg_frequency(cpu);
> +                       if (!hwp_active)
> +                               intel_pstate_adjust_busy_pstate(cpu);
> +               }
>         }
>  }
>
> @@ -1123,14 +1127,9 @@ static int intel_pstate_init_cpu(unsigne
>
>  static unsigned int intel_pstate_get(unsigned int cpu_num)
>  {
> -       struct sample *sample;
> -       struct cpudata *cpu;
> +       struct cpudata *cpu = all_cpu_data[cpu_num];
>
> -       cpu = all_cpu_data[cpu_num];
> -       if (!cpu)
> -               return 0;
> -       sample = &cpu->sample;
> -       return get_avg_frequency(cpu);
> +       return cpu ? cpu->avg_frequency : 0;
>  }
>
>  static void intel_pstate_set_update_util_hook(unsigned int cpu_num)
>



-- 
Regards,
Wanpeng Li