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| Started by | Prarit Bhargava <prarit@redhat.com> |
|---|---|
| First post | 2015-06-16 01:40 +0200 |
| Last post | 2015-06-16 23:20 +0200 |
| Articles | 3 — 2 participants |
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Re: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay [v2] Prarit Bhargava <prarit@redhat.com> - 2015-06-16 01:40 +0200
Re: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay [v2] "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-06-16 23:10 +0200
Re: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay [v2] "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-06-16 23:20 +0200
| From | Prarit Bhargava <prarit@redhat.com> |
|---|---|
| Date | 2015-06-16 01:40 +0200 |
| Subject | Re: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay [v2] |
| Message-ID | <pBM8V-1DN-17@gated-at.bofh.it> |
On 06/15/2015 06:12 PM, Kristen Carlson Accardi wrote:
> On Mon, 15 Jun 2015 13:43:29 -0400
> Prarit Bhargava <prarit@redhat.com> wrote:
>
>> The kernel may delay interrupts for a long time which can result in timers
>> being delayed. If this occurs the intel_pstate driver will crash with a
>> divide by zero error:
>>
>> divide error: 0000 [#1] SMP
>> Modules linked in: btrfs zlib_deflate raid6_pq xor msdos ext4 mbcache jbd2 binfmt_misc arc4 md4 nls_utf8 cifs dns_resolver tcp_lp bnep bluetooth rfkill fuse dm_service_time iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ftp ip6t_rpfilter ip6t_REJECT ipt_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw iptable_filter ip_tables intel_powerclamp coretemp vfat fat kvm_intel iTCO_wdt iTCO_vendor_support ipmi_devintf sr_mod kvm crct10dif_pclmul
>> crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel cdc_ether lrw usbnet cdrom mii gf128mul glue_helper ablk_helper cryptd lpc_ich mfd_core pcspkr sb_edac edac_core ipmi_si ipmi_msghandler ioatdma wmi shpchp acpi_pad nfsd auth_rpcgss nfs_acl lockd uinput dm_multipath sunrpc xfs libcrc32c usb_storage sd_mod crc_t10dif crct10dif_common ixgbe mgag200 syscopyarea sysfillrect sysimgblt mdio drm_kms_helper ttm igb drm ptp pps_core dca i2c_algo_bit megaraid_sas i2c_core dm_mirror dm_region_hash dm_log dm_mod
>> CPU: 113 PID: 0 Comm: swapper/113 Tainted: G W -------------- 3.10.0-229.1.2.el7.x86_64 #1
>> Hardware name: IBM x3950 X6 -[3837AC2]-/00FN827, BIOS -[A8E112BUS-1.00]- 08/27/2014
>> task: ffff880fe8abe660 ti: ffff880fe8ae4000 task.ti: ffff880fe8ae4000
>> RIP: 0010:[<ffffffff814a9279>] [<ffffffff814a9279>] intel_pstate_timer_func+0x179/0x3d0
>> RSP: 0018:ffff883fff4e3db8 EFLAGS: 00010206
>> RAX: 0000000027100000 RBX: ffff883fe6965100 RCX: 0000000000000000
>> RDX: 0000000000000000 RSI: 0000000000000010 RDI: 000000002e53632d
>> RBP: ffff883fff4e3e20 R08: 000e6f69a5a125c0 R09: ffff883fe84ec001
>> R10: 0000000000000002 R11: 0000000000000005 R12: 00000000000049f5
>> R13: 0000000000271000 R14: 00000000000049f5 R15: 0000000000000246
>> FS: 0000000000000000(0000) GS:ffff883fff4e0000(0000) knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007f7668601000 CR3: 000000000190a000 CR4: 00000000001407e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>> Stack:
>> ffff883fff4e3e58 ffffffff81099dc1 0000000000000086 0000000000000071
>> ffff883fff4f3680 0000000000000071 fbdc8a965e33afee ffffffff810b69dd
>> ffff883fe84ec000 ffff883fe6965108 0000000000000100 ffffffff814a9100
>> Call Trace:
>> <IRQ>
>>
>> [<ffffffff81099dc1>] ? run_posix_cpu_timers+0x51/0x840
>> [<ffffffff810b69dd>] ? trigger_load_balance+0x5d/0x200
>> [<ffffffff814a9100>] ? pid_param_set+0x130/0x130
>> [<ffffffff8107df56>] call_timer_fn+0x36/0x110
>> [<ffffffff814a9100>] ? pid_param_set+0x130/0x130
>> [<ffffffff8107fdcf>] run_timer_softirq+0x21f/0x320
>> [<ffffffff81077b2f>] __do_softirq+0xef/0x280
>> [<ffffffff816156dc>] call_softirq+0x1c/0x30
>> [<ffffffff81015d95>] do_softirq+0x65/0xa0
>> [<ffffffff81077ec5>] irq_exit+0x115/0x120
>> [<ffffffff81616355>] smp_apic_timer_interrupt+0x45/0x60
>> [<ffffffff81614a1d>] apic_timer_interrupt+0x6d/0x80
>> <EOI>
>>
>> [<ffffffff814a9c32>] ? cpuidle_enter_state+0x52/0xc0
>> [<ffffffff814a9c28>] ? cpuidle_enter_state+0x48/0xc0
>> [<ffffffff814a9d65>] cpuidle_idle_call+0xc5/0x200
>> [<ffffffff8101d14e>] arch_cpu_idle+0xe/0x30
>> [<ffffffff810c67c1>] cpu_startup_entry+0xf1/0x290
>> [<ffffffff8104228a>] start_secondary+0x1ba/0x230
>> Code: 42 0f 00 45 89 e6 48 01 c2 43 8d 44 6d 00 39 d0 73 26 49 c1 e5 08 89 d2 4d 63 f4 49 63 c5 48 c1 e2 08 48 c1 e0 08 48 63 ca 48 99 <48> f7 f9 48 98 4c 0f af f0 49 c1 ee 08 8b 43 78 c1 e0 08 44 29
>> RIP [<ffffffff814a9279>] intel_pstate_timer_func+0x179/0x3d0
>> RSP <ffff883fff4e3db8>
>>
>> The kernel values for cpudata for CPU 113 were:
>>
>> struct cpudata {
>> cpu = 113,
>> timer = {
>> entry = {
>> next = 0x0,
>> prev = 0xdead000000200200
>> },
>> expires = 8357799745,
>> base = 0xffff883fe84ec001,
>> function = 0xffffffff814a9100 <intel_pstate_timer_func>,
>> data = 18446612406765768960,
>> <snip>
>> i_gain = 0,
>> d_gain = 0,
>> deadband = 0,
>> last_err = 22489
>> },
>> last_sample_time = {
>> tv64 = 4063132438017305
>> },
>> prev_aperf = 287326796397463,
>> prev_mperf = 251427432090198,
>> sample = {
>> core_pct_busy = 23081,
>> aperf = 2937407,
>> mperf = 3257884,
>> freq = 2524484,
>> time = {
>> tv64 = 4063149215234118
>> }
>> }
>> }
>>
>> which results in the time between samples = last_sample_time - sample.time
>> = 4063149215234118 - 4063132438017305 = 16777216813 which is 16.777 seconds.
>>
>> The duration between reads of the APERF and MPERF registers overflowed a s32
>> sized integer in intel_pstate_get_scaled_busy()'s call to div_fp(). The result
>> is that int_tofp(duration_us) == 0, and the kernel attempts to divide by 0.
>>
>> While the kernel shouldn't be delaying for a long time, it can and does
>> happen and the intel_pstate driver should not panic in this situation. This
>> patch changes the div_fp() function to use div64_s64() to allow for "long"
>> division. This will avoid the overflow condition on long delays.
>>
>> [v2]: use div64_s64() in div_fp()
>
> Were you able to resolve your original concerns with doing this? I
> thought you mentioned that you'd tested it and it gave you some
> negative side effects?
Sorry Kristen, I think my comment confused you. I was worried about passing "0"
back as the core_busy value after a long delay. Given that it is already
possible to return 0 when the duration exceeds 3 * the expected delay I no
longer think there is any issue of returning 0 on a _really really really long_
delay.
IOW, there isn't a problem and I was being overly careful with v1 of the patch.
P.
>
> Thanks,
> Kristen
>
>>
>> Cc: Kristen Carlson Accardi <kristen@linux.intel.com>
>> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
>> Cc: Viresh Kumar <viresh.kumar@linaro.org>
>> Cc: Doug Smythies <dsmythies@telus.net>
>> Cc: linux-pm@vger.kernel.org
>>
>> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
>> ---
>> drivers/cpufreq/intel_pstate.c | 10 +++++-----
>> 1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
>> index 6414661..b153d86 100644
>> --- a/drivers/cpufreq/intel_pstate.c
>> +++ b/drivers/cpufreq/intel_pstate.c
>> @@ -48,9 +48,9 @@ static inline int32_t mul_fp(int32_t x, int32_t y)
>> return ((int64_t)x * (int64_t)y) >> FRAC_BITS;
>> }
>>
>> -static inline int32_t div_fp(int32_t x, int32_t y)
>> +static inline int32_t div_fp(s64 x, s64 y)
>> {
>> - return div_s64((int64_t)x << FRAC_BITS, y);
>> + return div64_s64((int64_t)x << FRAC_BITS, y);
>> }
>>
>> static inline int ceiling_fp(int32_t x)
>> @@ -794,7 +794,7 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
>> static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)
>> {
>> int32_t core_busy, max_pstate, current_pstate, sample_ratio;
>> - u32 duration_us;
>> + s64 duration_us;
>> u32 sample_time;
>>
>> /*
>> @@ -821,8 +821,8 @@ static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu)
>> * to adjust our busyness.
>> */
>> sample_time = pid_params.sample_rate_ms * USEC_PER_MSEC;
>> - duration_us = (u32) ktime_us_delta(cpu->sample.time,
>> - cpu->last_sample_time);
>> + duration_us = ktime_us_delta(cpu->sample.time,
>> + cpu->last_sample_time);
>> if (duration_us > sample_time * 3) {
>> sample_ratio = div_fp(int_tofp(sample_time),
>> int_tofp(duration_us));
>
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| From | "Rafael J. Wysocki" <rjw@rjwysocki.net> |
|---|---|
| Date | 2015-06-16 23:10 +0200 |
| Subject | Re: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay [v2] |
| Message-ID | <pC6hk-5N6-15@gated-at.bofh.it> |
| In reply to | #1165605 |
On Monday, June 15, 2015 07:33:03 PM Prarit Bhargava wrote:
>
> On 06/15/2015 06:12 PM, Kristen Carlson Accardi wrote:
> > On Mon, 15 Jun 2015 13:43:29 -0400
> > Prarit Bhargava <prarit@redhat.com> wrote:
> >
> >> The kernel may delay interrupts for a long time which can result in timers
> >> being delayed. If this occurs the intel_pstate driver will crash with a
> >> divide by zero error:
> >>
> >> divide error: 0000 [#1] SMP
> >> Modules linked in: btrfs zlib_deflate raid6_pq xor msdos ext4 mbcache jbd2 binfmt_misc arc4 md4 nls_utf8 cifs dns_resolver tcp_lp bnep bluetooth rfkill fuse dm_service_time iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ftp ip6t_rpfilter ip6t_REJECT ipt_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw iptable_filter ip_tables intel_powerclamp coretemp vfat fat kvm_intel iTCO_wdt iTCO_vendor_support ipmi_devintf sr_mod kvm crct10dif_pclmul
> >> crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel cdc_ether lrw usbnet cdrom mii gf128mul glue_helper ablk_helper cryptd lpc_ich mfd_core pcspkr sb_edac edac_core ipmi_si ipmi_msghandler ioatdma wmi shpchp acpi_pad nfsd auth_rpcgss nfs_acl lockd uinput dm_multipath sunrpc xfs libcrc32c usb_storage sd_mod crc_t10dif crct10dif_common ixgbe mgag200 syscopyarea sysfillrect sysimgblt mdio drm_kms_helper ttm igb drm ptp pps_core dca i2c_algo_bit megaraid_sas i2c_core dm_mirror dm_region_hash dm_log dm_mod
> >> CPU: 113 PID: 0 Comm: swapper/113 Tainted: G W -------------- 3.10.0-229.1.2.el7.x86_64 #1
> >> Hardware name: IBM x3950 X6 -[3837AC2]-/00FN827, BIOS -[A8E112BUS-1.00]- 08/27/2014
> >> task: ffff880fe8abe660 ti: ffff880fe8ae4000 task.ti: ffff880fe8ae4000
> >> RIP: 0010:[<ffffffff814a9279>] [<ffffffff814a9279>] intel_pstate_timer_func+0x179/0x3d0
> >> RSP: 0018:ffff883fff4e3db8 EFLAGS: 00010206
> >> RAX: 0000000027100000 RBX: ffff883fe6965100 RCX: 0000000000000000
> >> RDX: 0000000000000000 RSI: 0000000000000010 RDI: 000000002e53632d
> >> RBP: ffff883fff4e3e20 R08: 000e6f69a5a125c0 R09: ffff883fe84ec001
> >> R10: 0000000000000002 R11: 0000000000000005 R12: 00000000000049f5
> >> R13: 0000000000271000 R14: 00000000000049f5 R15: 0000000000000246
> >> FS: 0000000000000000(0000) GS:ffff883fff4e0000(0000) knlGS:0000000000000000
> >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: 00007f7668601000 CR3: 000000000190a000 CR4: 00000000001407e0
> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> >> Stack:
> >> ffff883fff4e3e58 ffffffff81099dc1 0000000000000086 0000000000000071
> >> ffff883fff4f3680 0000000000000071 fbdc8a965e33afee ffffffff810b69dd
> >> ffff883fe84ec000 ffff883fe6965108 0000000000000100 ffffffff814a9100
> >> Call Trace:
> >> <IRQ>
> >>
> >> [<ffffffff81099dc1>] ? run_posix_cpu_timers+0x51/0x840
> >> [<ffffffff810b69dd>] ? trigger_load_balance+0x5d/0x200
> >> [<ffffffff814a9100>] ? pid_param_set+0x130/0x130
> >> [<ffffffff8107df56>] call_timer_fn+0x36/0x110
> >> [<ffffffff814a9100>] ? pid_param_set+0x130/0x130
> >> [<ffffffff8107fdcf>] run_timer_softirq+0x21f/0x320
> >> [<ffffffff81077b2f>] __do_softirq+0xef/0x280
> >> [<ffffffff816156dc>] call_softirq+0x1c/0x30
> >> [<ffffffff81015d95>] do_softirq+0x65/0xa0
> >> [<ffffffff81077ec5>] irq_exit+0x115/0x120
> >> [<ffffffff81616355>] smp_apic_timer_interrupt+0x45/0x60
> >> [<ffffffff81614a1d>] apic_timer_interrupt+0x6d/0x80
> >> <EOI>
> >>
> >> [<ffffffff814a9c32>] ? cpuidle_enter_state+0x52/0xc0
> >> [<ffffffff814a9c28>] ? cpuidle_enter_state+0x48/0xc0
> >> [<ffffffff814a9d65>] cpuidle_idle_call+0xc5/0x200
> >> [<ffffffff8101d14e>] arch_cpu_idle+0xe/0x30
> >> [<ffffffff810c67c1>] cpu_startup_entry+0xf1/0x290
> >> [<ffffffff8104228a>] start_secondary+0x1ba/0x230
> >> Code: 42 0f 00 45 89 e6 48 01 c2 43 8d 44 6d 00 39 d0 73 26 49 c1 e5 08 89 d2 4d 63 f4 49 63 c5 48 c1 e2 08 48 c1 e0 08 48 63 ca 48 99 <48> f7 f9 48 98 4c 0f af f0 49 c1 ee 08 8b 43 78 c1 e0 08 44 29
> >> RIP [<ffffffff814a9279>] intel_pstate_timer_func+0x179/0x3d0
> >> RSP <ffff883fff4e3db8>
> >>
> >> The kernel values for cpudata for CPU 113 were:
> >>
> >> struct cpudata {
> >> cpu = 113,
> >> timer = {
> >> entry = {
> >> next = 0x0,
> >> prev = 0xdead000000200200
> >> },
> >> expires = 8357799745,
> >> base = 0xffff883fe84ec001,
> >> function = 0xffffffff814a9100 <intel_pstate_timer_func>,
> >> data = 18446612406765768960,
> >> <snip>
> >> i_gain = 0,
> >> d_gain = 0,
> >> deadband = 0,
> >> last_err = 22489
> >> },
> >> last_sample_time = {
> >> tv64 = 4063132438017305
> >> },
> >> prev_aperf = 287326796397463,
> >> prev_mperf = 251427432090198,
> >> sample = {
> >> core_pct_busy = 23081,
> >> aperf = 2937407,
> >> mperf = 3257884,
> >> freq = 2524484,
> >> time = {
> >> tv64 = 4063149215234118
> >> }
> >> }
> >> }
> >>
> >> which results in the time between samples = last_sample_time - sample.time
> >> = 4063149215234118 - 4063132438017305 = 16777216813 which is 16.777 seconds.
> >>
> >> The duration between reads of the APERF and MPERF registers overflowed a s32
> >> sized integer in intel_pstate_get_scaled_busy()'s call to div_fp(). The result
> >> is that int_tofp(duration_us) == 0, and the kernel attempts to divide by 0.
> >>
> >> While the kernel shouldn't be delaying for a long time, it can and does
> >> happen and the intel_pstate driver should not panic in this situation. This
> >> patch changes the div_fp() function to use div64_s64() to allow for "long"
> >> division. This will avoid the overflow condition on long delays.
> >>
> >> [v2]: use div64_s64() in div_fp()
> >
> > Were you able to resolve your original concerns with doing this? I
> > thought you mentioned that you'd tested it and it gave you some
> > negative side effects?
>
> Sorry Kristen, I think my comment confused you. I was worried about passing "0"
> back as the core_busy value after a long delay. Given that it is already
> possible to return 0 when the duration exceeds 3 * the expected delay I no
> longer think there is any issue of returning 0 on a _really really really long_
> delay.
>
> IOW, there isn't a problem and I was being overly careful with v1 of the patch.
OK, patch queued up fo 4.1, thanks!
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
--
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[toc] | [prev] | [next] | [standalone]
| From | "Rafael J. Wysocki" <rjw@rjwysocki.net> |
|---|---|
| Date | 2015-06-16 23:20 +0200 |
| Subject | Re: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay [v2] |
| Message-ID | <pC6r0-5Yu-21@gated-at.bofh.it> |
| In reply to | #1166407 |
On Tuesday, June 16, 2015 11:35:10 PM Rafael J. Wysocki wrote:
> On Monday, June 15, 2015 07:33:03 PM Prarit Bhargava wrote:
> >
> > On 06/15/2015 06:12 PM, Kristen Carlson Accardi wrote:
> > > On Mon, 15 Jun 2015 13:43:29 -0400
> > > Prarit Bhargava <prarit@redhat.com> wrote:
> > >
> > >> The kernel may delay interrupts for a long time which can result in timers
> > >> being delayed. If this occurs the intel_pstate driver will crash with a
> > >> divide by zero error:
> > >>
> > >> divide error: 0000 [#1] SMP
> > >> Modules linked in: btrfs zlib_deflate raid6_pq xor msdos ext4 mbcache jbd2 binfmt_misc arc4 md4 nls_utf8 cifs dns_resolver tcp_lp bnep bluetooth rfkill fuse dm_service_time iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ftp ip6t_rpfilter ip6t_REJECT ipt_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw iptable_filter ip_tables intel_powerclamp coretemp vfat fat kvm_intel iTCO_wdt iTCO_vendor_support ipmi_devintf sr_mod kvm crct10dif_pclmul
> > >> crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel cdc_ether lrw usbnet cdrom mii gf128mul glue_helper ablk_helper cryptd lpc_ich mfd_core pcspkr sb_edac edac_core ipmi_si ipmi_msghandler ioatdma wmi shpchp acpi_pad nfsd auth_rpcgss nfs_acl lockd uinput dm_multipath sunrpc xfs libcrc32c usb_storage sd_mod crc_t10dif crct10dif_common ixgbe mgag200 syscopyarea sysfillrect sysimgblt mdio drm_kms_helper ttm igb drm ptp pps_core dca i2c_algo_bit megaraid_sas i2c_core dm_mirror dm_region_hash dm_log dm_mod
> > >> CPU: 113 PID: 0 Comm: swapper/113 Tainted: G W -------------- 3.10.0-229.1.2.el7.x86_64 #1
> > >> Hardware name: IBM x3950 X6 -[3837AC2]-/00FN827, BIOS -[A8E112BUS-1.00]- 08/27/2014
> > >> task: ffff880fe8abe660 ti: ffff880fe8ae4000 task.ti: ffff880fe8ae4000
> > >> RIP: 0010:[<ffffffff814a9279>] [<ffffffff814a9279>] intel_pstate_timer_func+0x179/0x3d0
> > >> RSP: 0018:ffff883fff4e3db8 EFLAGS: 00010206
> > >> RAX: 0000000027100000 RBX: ffff883fe6965100 RCX: 0000000000000000
> > >> RDX: 0000000000000000 RSI: 0000000000000010 RDI: 000000002e53632d
> > >> RBP: ffff883fff4e3e20 R08: 000e6f69a5a125c0 R09: ffff883fe84ec001
> > >> R10: 0000000000000002 R11: 0000000000000005 R12: 00000000000049f5
> > >> R13: 0000000000271000 R14: 00000000000049f5 R15: 0000000000000246
> > >> FS: 0000000000000000(0000) GS:ffff883fff4e0000(0000) knlGS:0000000000000000
> > >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > >> CR2: 00007f7668601000 CR3: 000000000190a000 CR4: 00000000001407e0
> > >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > >> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > >> Stack:
> > >> ffff883fff4e3e58 ffffffff81099dc1 0000000000000086 0000000000000071
> > >> ffff883fff4f3680 0000000000000071 fbdc8a965e33afee ffffffff810b69dd
> > >> ffff883fe84ec000 ffff883fe6965108 0000000000000100 ffffffff814a9100
> > >> Call Trace:
> > >> <IRQ>
> > >>
> > >> [<ffffffff81099dc1>] ? run_posix_cpu_timers+0x51/0x840
> > >> [<ffffffff810b69dd>] ? trigger_load_balance+0x5d/0x200
> > >> [<ffffffff814a9100>] ? pid_param_set+0x130/0x130
> > >> [<ffffffff8107df56>] call_timer_fn+0x36/0x110
> > >> [<ffffffff814a9100>] ? pid_param_set+0x130/0x130
> > >> [<ffffffff8107fdcf>] run_timer_softirq+0x21f/0x320
> > >> [<ffffffff81077b2f>] __do_softirq+0xef/0x280
> > >> [<ffffffff816156dc>] call_softirq+0x1c/0x30
> > >> [<ffffffff81015d95>] do_softirq+0x65/0xa0
> > >> [<ffffffff81077ec5>] irq_exit+0x115/0x120
> > >> [<ffffffff81616355>] smp_apic_timer_interrupt+0x45/0x60
> > >> [<ffffffff81614a1d>] apic_timer_interrupt+0x6d/0x80
> > >> <EOI>
> > >>
> > >> [<ffffffff814a9c32>] ? cpuidle_enter_state+0x52/0xc0
> > >> [<ffffffff814a9c28>] ? cpuidle_enter_state+0x48/0xc0
> > >> [<ffffffff814a9d65>] cpuidle_idle_call+0xc5/0x200
> > >> [<ffffffff8101d14e>] arch_cpu_idle+0xe/0x30
> > >> [<ffffffff810c67c1>] cpu_startup_entry+0xf1/0x290
> > >> [<ffffffff8104228a>] start_secondary+0x1ba/0x230
> > >> Code: 42 0f 00 45 89 e6 48 01 c2 43 8d 44 6d 00 39 d0 73 26 49 c1 e5 08 89 d2 4d 63 f4 49 63 c5 48 c1 e2 08 48 c1 e0 08 48 63 ca 48 99 <48> f7 f9 48 98 4c 0f af f0 49 c1 ee 08 8b 43 78 c1 e0 08 44 29
> > >> RIP [<ffffffff814a9279>] intel_pstate_timer_func+0x179/0x3d0
> > >> RSP <ffff883fff4e3db8>
> > >>
> > >> The kernel values for cpudata for CPU 113 were:
> > >>
> > >> struct cpudata {
> > >> cpu = 113,
> > >> timer = {
> > >> entry = {
> > >> next = 0x0,
> > >> prev = 0xdead000000200200
> > >> },
> > >> expires = 8357799745,
> > >> base = 0xffff883fe84ec001,
> > >> function = 0xffffffff814a9100 <intel_pstate_timer_func>,
> > >> data = 18446612406765768960,
> > >> <snip>
> > >> i_gain = 0,
> > >> d_gain = 0,
> > >> deadband = 0,
> > >> last_err = 22489
> > >> },
> > >> last_sample_time = {
> > >> tv64 = 4063132438017305
> > >> },
> > >> prev_aperf = 287326796397463,
> > >> prev_mperf = 251427432090198,
> > >> sample = {
> > >> core_pct_busy = 23081,
> > >> aperf = 2937407,
> > >> mperf = 3257884,
> > >> freq = 2524484,
> > >> time = {
> > >> tv64 = 4063149215234118
> > >> }
> > >> }
> > >> }
> > >>
> > >> which results in the time between samples = last_sample_time - sample.time
> > >> = 4063149215234118 - 4063132438017305 = 16777216813 which is 16.777 seconds.
> > >>
> > >> The duration between reads of the APERF and MPERF registers overflowed a s32
> > >> sized integer in intel_pstate_get_scaled_busy()'s call to div_fp(). The result
> > >> is that int_tofp(duration_us) == 0, and the kernel attempts to divide by 0.
> > >>
> > >> While the kernel shouldn't be delaying for a long time, it can and does
> > >> happen and the intel_pstate driver should not panic in this situation. This
> > >> patch changes the div_fp() function to use div64_s64() to allow for "long"
> > >> division. This will avoid the overflow condition on long delays.
> > >>
> > >> [v2]: use div64_s64() in div_fp()
> > >
> > > Were you able to resolve your original concerns with doing this? I
> > > thought you mentioned that you'd tested it and it gave you some
> > > negative side effects?
> >
> > Sorry Kristen, I think my comment confused you. I was worried about passing "0"
> > back as the core_busy value after a long delay. Given that it is already
> > possible to return 0 when the duration exceeds 3 * the expected delay I no
> > longer think there is any issue of returning 0 on a _really really really long_
> > delay.
> >
> > IOW, there isn't a problem and I was being overly careful with v1 of the patch.
>
> OK, patch queued up fo 4.1, thanks!
That should have been 4.2, sorry.
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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