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

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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@kernel.org> wrote:
> > On Tue, May 3, 2016 at 2:54 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> >> On Tue, May 3, 2016 at 2:15 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> >>> On Tue, May 3, 2016 at 10:32 AM, Peter Zijlstra <peterz@infradead.org> 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.

---
 drivers/cpufreq/intel_pstate.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 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;
 };
 
@@ -1037,6 +1038,7 @@ static inline void intel_pstate_adjust_b
 	intel_pstate_update_pstate(cpu, target_pstate);
 
 	sample = &cpu->sample;
+	cpu->avg_frequency = get_avg_frequency(cpu);
 	trace_pstate_sample(fp_toint(sample->core_pct_busy),
 		fp_toint(sample->busy_scaled),
 		from,
@@ -1044,7 +1046,7 @@ 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,
@@ -1130,7 +1132,7 @@ static unsigned int intel_pstate_get(uns
 	if (!cpu)
 		return 0;
 	sample = &cpu->sample;
-	return get_avg_frequency(cpu);
+	return cpu->avg_frequency;
 }
 
 static void intel_pstate_set_update_util_hook(unsigned int cpu_num)