From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755765AbdLTRAy (ORCPT ); Wed, 20 Dec 2017 12:00:54 -0500 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:3720 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755542AbdLTRAx (ORCPT ); Wed, 20 Dec 2017 12:00:53 -0500 X-IronPort-AV: E=Sophos;i="5.45,432,1508803200"; d="scan'208";a="581720146" From: "Sironi, Filippo" To: Peter Zijlstra CC: "linux-kernel@vger.kernel.org" , "mingo@redhat.com" Subject: Re: [PATCH] sched/fair: Prevent a division by 0 in scale_rt_capacity() Thread-Topic: [PATCH] sched/fair: Prevent a division by 0 in scale_rt_capacity() Thread-Index: AQHTcMRShCgoohe6EUuIbJFfhutdHaNLHuMAgAFjhYA= Date: Wed, 20 Dec 2017 16:45:42 +0000 Message-ID: <80DE0B49-BAF8-42F5-93DF-4B4890DD8090@amazon.de> References: <1512806629-27072-1-git-send-email-sironi@amazon.de> <20171219193314.2wxiehzquoea5dnr@hirez.programming.kicks-ass.net> In-Reply-To: <20171219193314.2wxiehzquoea5dnr@hirez.programming.kicks-ass.net> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.43.164.59] Content-Type: text/plain; charset="us-ascii" Content-ID: <4CCAA7C2FAD81D48A36C22ADF9494796@amazon.com> MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id vBKH100e021420 > On 19. Dec 2017, at 20:33, Peter Zijlstra wrote: > > On Sat, Dec 09, 2017 at 09:03:49AM +0100, Filippo Sironi wrote: >> ... since total = sched_avg_period() + delta can yield 0x100000000, >> which results in a division by 0, given that div_u64() takes a u32 >> divisor. Use div64_u64() instead. >> >> divide error: 0000 [#1] SMP >> CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.9.58 #1 >> Hardware name: ... >> task: ffff8800a24e2800 task.stack: ffffc9000074c000 >> RIP: 0010:[] [] update_group_capacity+0x16e/0x1c0 >> RSP: 0018:ffff8800a74e3c18 EFLAGS: 00010246 >> RAX: 0000000000445ced RBX: 0000000000000007 RCX: 000000000000024d >> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000000160c0 >> RBP: ffff8800a74e3c38 R08: ffff8800a17d5ac0 R09: ffff8800a74e0000 >> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800a297e400 >> R13: ffff8800a17d5ac0 R14: 0000000000000000 R15: ffff8800a17d5ac0 >> FS: 0000000000000000(0000) GS:ffff8800a74e0000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 00000000006f3580 CR3: 0000000001607000 CR4: 00000000007426e0 >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> PKRU: 55555554 >> Stack: >> ffff8800a17d5180 ffff8800a74e3e00 ffff8800a17d5a01 ffff8800a74e3c68 >> ffff8800a74e3d90 ffffffff810d37e6 fffffffffffffff8 0000002300010c40 >> 0000000000000040 ffff8800a17d5ad8 0000000000000000 0000000000000000 >> Call Trace: >> [162553.008569] [] find_busiest_group+0xe6/0x950 >> [] load_balance+0x188/0xa70 >> [] ? update_rq_clock.part.88+0x13/0x30 >> [] rebalance_domains+0x210/0x290 >> [] run_rebalance_domains+0x1b0/0x1d0 >> [] __do_softirq+0x89/0x2b0 >> [] irq_exit+0xab/0xb0 >> [] smp_reschedule_interrupt+0x2e/0x30 >> [] reschedule_interrupt+0x84/0x90 >> [162553.008603] [] ? cpuidle_enter_state+0x12f/0x2c0 >> [] cpuidle_enter+0x12/0x20 >> [] cpu_startup_entry+0x1a2/0x1f0 >> [] start_secondary+0x12d/0x140 >> Code: 0f 00 4c 8b 96 48 09 00 00 48 8b 86 40 09 00 00 48 8b b6 b0 08 00 00 48 d1 ea 4c 29 d6 41 ba 00 00 00 00 49 0f 48 f2 01 d6 31 d2 <48> f7 f6 ba 00 04 00 00 48 29 c2 48 3d ff 03 00 00 b8 01 00 00 >> RIP [] update_group_capacity+0x16e/0x1c0 >> RSP >> >> Cc: Ingo Molnar >> Cc: Peter Zijlstra >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Filippo Sironi >> --- >> kernel/sched/fair.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 4037e19bbca2..04b6f847a241 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -7517,7 +7517,7 @@ static unsigned long scale_rt_capacity(int cpu) >> >> total = sched_avg_period() + delta; >> >> - used = div_u64(avg, total); >> + used = div64_u64(avg, total); >> > > so total should not get larger than 2*period IIRC, how did we get so > large? > >>From the vmcores I got, it was always delta that made it become very large. Amazon Development Center Germany GmbH Berlin - Dresden - Aachen main office: Krausenstr. 38, 10117 Berlin Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger Ust-ID: DE289237879 Eingetragen am Amtsgericht Charlottenburg HRB 149173 B