Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756794AbbFPVJ7 (ORCPT ); Tue, 16 Jun 2015 17:09:59 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:41830 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754764AbbFPVJu (ORCPT ); Tue, 16 Jun 2015 17:09:50 -0400 From: "Rafael J. Wysocki" To: Prarit Bhargava Cc: Kristen Carlson Accardi , linux-kernel@vger.kernel.org, Viresh Kumar , Doug Smythies , linux-pm@vger.kernel.org Subject: Re: [PATCH] cpufreq, Fix overflow in busy_scaled due to long delay [v2] Date: Tue, 16 Jun 2015 23:35:48 +0200 Message-ID: <7403941.Btu4pSCGus@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.1.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <1584292.keTKsQ78Dn@vostro.rjw.lan> References: <1434390209-23256-1-git-send-email-prarit@redhat.com> <557F60AF.7070609@redhat.com> <1584292.keTKsQ78Dn@vostro.rjw.lan> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7377 Lines: 134 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 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:[] [] 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: > > >> > > >> > > >> [] ? run_posix_cpu_timers+0x51/0x840 > > >> [] ? trigger_load_balance+0x5d/0x200 > > >> [] ? pid_param_set+0x130/0x130 > > >> [] call_timer_fn+0x36/0x110 > > >> [] ? pid_param_set+0x130/0x130 > > >> [] run_timer_softirq+0x21f/0x320 > > >> [] __do_softirq+0xef/0x280 > > >> [] call_softirq+0x1c/0x30 > > >> [] do_softirq+0x65/0xa0 > > >> [] irq_exit+0x115/0x120 > > >> [] smp_apic_timer_interrupt+0x45/0x60 > > >> [] apic_timer_interrupt+0x6d/0x80 > > >> > > >> > > >> [] ? cpuidle_enter_state+0x52/0xc0 > > >> [] ? cpuidle_enter_state+0x48/0xc0 > > >> [] cpuidle_idle_call+0xc5/0x200 > > >> [] arch_cpu_idle+0xe/0x30 > > >> [] cpu_startup_entry+0xf1/0x290 > > >> [] 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 [] intel_pstate_timer_func+0x179/0x3d0 > > >> RSP > > >> > > >> 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 , > > >> data = 18446612406765768960, > > >> > > >> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/