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

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Message-ID: <CAJZ5v0gmsJ+SWR4twQ-A2oARthOQkh5umj67Sfyq3L3ZVRZ2Yw@mail.gmail.com>
Date:	Tue, 3 May 2016 15:33:27 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	kernel test robot <ying.huang@...ux.intel.com>,
	Steve Muckle <steve.muckle@...aro.org>, lkp@...org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Mike Galbraith <efault@....de>,
	Michael Turquette <mturquette@...libre.com>,
	Juri Lelli <Juri.Lelli@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steve Muckle <smuckle@...aro.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [lkp] [sched/fair] 41e0d37f7a: divide error: 0000 [#1] SMP

On Tue, May 3, 2016 at 11:25 AM, Wanpeng Li <kernellwp@...il.com> wrote:
> 2016-05-03 17:19 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
>> 2016-05-03 16:32 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
>>> 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.
>>
>> I think one sample should be called during intel_pstate driver
>> initialization, how about the below patch(untested)?
>>
>> ----snip----
>>
>> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
>> index 8b5a415..57b3843 100644
>> --- a/drivers/cpufreq/intel_pstate.c
>> +++ b/drivers/cpufreq/intel_pstate.c
>> @@ -1241,6 +1241,7 @@ static int intel_pstate_init_cpu(unsigned int cpunum)
>>         intel_pstate_get_cpu_pstates(cpu);
>>
>>         intel_pstate_busy_pid_reset(cpu);
>> +       intel_pstate_sample(cpu);
>
> intel_pstate_sample(cpu, 0);
>
>>
>>         cpu->update_util.func = intel_pstate_update_util;

That would avoid the divide by 0, but the value returned by
intel_pstate_get() would still be bogus.