linux-kernel - Re: 答复: [????] Re: divide error in x86 and cputime

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <518a5712-3348-4acd-ae26-529621143ef7@huawei.com>
Date: Sun, 4 Jan 2026 21:23:07 +0800
From: Xia Fukun <xiafukun@...wei.com>
To: "Li,Rongqing" <lirongqing@...du.com>, Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, David Laight
	<david.laight.linux@...il.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vschneid@...hat.com" <vschneid@...hat.com>, "mgorman@...e.de"
	<mgorman@...e.de>, "bsegall@...gle.com" <bsegall@...gle.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>, "dietmar.eggemann@....com"
	<dietmar.eggemann@....com>, "vincent.guittot@...aro.org"
	<vincent.guittot@...aro.org>, "juri.lelli@...hat.com"
	<juri.lelli@...hat.com>, "mingo@...hat.com" <mingo@...hat.com>, "Zhangqiao
 (2012 lab)" <zhangqiao22@...wei.com>, Xia Fukun <xiafukun@...wei.com>
Subject: Re: 答复: [????] Re: divide error in x86 and cputime


On 7/8/2025 7:41 AM, Li,Rongqing wrote:
> 
> it happened when a process with 236 busy polling threads , run about 904 days, the total time will overflow the 64bit
> 
> non-x86 system maybe has same issue, once (stime + utime) overflows 64bit, mul_u64_u64_div_u64 from lib/math/div64.c maybe cause division by 0
> 

We have encountered the same issue in an environment with x86 architecture and kernel version 5.10.

[48734536.498953] divide error: 0000 [#1] SMP NOPTI
[48734536.504336] CPU: 273 PID: 4619 Comm: nano-sysmonitor Kdump: loaded Tainted: G           OE     5.10.0-60.18.0.50.r1209_60_175.hce2.x86_64 #1
[48734536.518065] Hardware name: XFUSION 5885H V7/BC15MBHA, BIOS 01.02.01.03 01/01/2024
[48734536.526620] RIP: 0010:cputime_adjust+0x55/0xb0
[48734536.532093] Code: 0b 48 8b 7d 10 49 89 c0 48 8d 04 0e 48 39 f8 73 38 48 8b 45 00 48 8b 55 08 48 85 c0 74 16 48 85 d2 74 4d 4c 8d 0c 10 48 f7 e7 <49> f7 f1 48 39 c6 48 0f 42 f0 48 89 f8 48 29 f0 48 39 c1 77 29 48
[48734536.552057] RSP: 0018:ffffae408e07bbc8 EFLAGS: 00010807
[48734536.558328] RAX: 2facb95ea704eb6a RBX: ffff98b6293db180 RCX: fff9b822b886cabf
[48734536.566529] RDX: 0005cf0f135b9489 RSI: 0005cf0ec21afa94 RDI: ffff93c922ae82ee
[48734536.574727] RBP: ffffae408e07bbf8 R08: 0000000000000082 R09: 000007333e295d49
[48734536.582930] R10: 8000000000000000 R11: 0000000000000000 R12: ffffae408e07bcf8
[48734536.591131] R13: ffffae408e07bcf0 R14: ffff98b6293db190 R15: fffa2e80e26a98fd
[48734536.599334] FS:  00007f0bc58c3740(0000) GS:ffff98bb75040000(0000) knlGS:0000000000000000
[48734536.608498] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[48734536.615294] CR2: 0000557c0ddca1c8 CR3: 00000600ae12a002 CR4: 0000000000372ee0
[48734536.623497] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[48734536.631697] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
[48734536.639898] Call Trace:
[48734536.712624]  thread_group_cputime_adjusted+0x4b/0x70
[48734536.718634]  do_task_stat+0x2d8/0xdc0
[48734536.723326]  task_info_proc_get_info+0x133/0x150


Specifically, a division error occurs in cputime_adjust() during the following calculation:

mul_u64_u64_div_u64(0x5cf1187f5ad33, 0xffff93c922ae82ee, 0x7333e295d49)

Is the patch provided here feasible? Or are there any known workarounds?

> so to cputime, could cputime_adjust() return stime if stime if stime + utime is overflow
> 
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 6dab4854..db0c273 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -579,6 +579,10 @@ void cputime_adjust(struct task_cputime *curr, struct prev_cputime *prev,
>                 goto update;
>         }
> 
> +       if (stime > (stime + utime)) {
> +               goto update;
> +       }
> +
>         stime = mul_u64_u64_div_u64(stime, rtime, stime + utime);
>         /*
>          * Because mul_u64_u64_div_u64() can approximate on some
>