divide error in x86 and cputime

["Li,Rongqing" <lirongqing@baidu.com>]

Hi:

I see a divide error on x86 machine, the stack is below:


[78250815.703847] divide error: 0000 [#1] PREEMPT SMP NOPTI
[78250815.703852] CPU: 127 PID: 83435 Comm: killall Kdump: loaded Tainted: P           OE K   5.10.0 #1
[78250815.703853] Hardware name: Inspur SSINSPURMBX-XA3-100D-B356/NF5280A6, BIOS 3.00.21 06/27/2022
[78250815.703859] RIP: 0010:cputime_adjust+0x55/0xb0
[78250815.703860] Code: 3b 4c 8b 4d 10 48 89 c6 49 8d 04 38 4c 39 c8 73 38 48 8b 45 00 48 8b 55 08 48 85 c0 74 16 48 85 d2 74 49 48 8d 0c 10 49 f7 e1 <48> f7 f1 49 39 c0 4c 0f 42 c0 4c 89 c8 4c 29 c0 48 39 c7 77 25 48
[78250815.703861] RSP: 0018:ffffa34c2517bc40 EFLAGS: 00010887
[78250815.703864] RAX: 69f98da9ba980c00 RBX: ffff976c93d2a5e0 RCX: 0000000709e00900
[78250815.703864] RDX: 00f5dfffab0fc352 RSI: 0000000000000082 RDI: ff07410dca0bcd5e
[78250815.703865] RBP: ffffa34c2517bc70 R08: 00f5dfff54f8e5ce R09: fffd213aabd74626
[78250815.703866] R10: ffffa34c2517bed8 R11: 0000000000000000 R12: ffff976c93d2a5f0
[78250815.703867] R13: ffffa34c2517bd78 R14: ffffa34c2517bd70 R15: 0000000000001000
[78250815.703868] FS:  00007f58060f97a0(0000) GS:ffff976afe9c0000(0000) knlGS:0000000000000000
[78250815.703869] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[78250815.703870] CR2: 00007f580610e000 CR3: 0000017e3b3d2004 CR4: 0000000000770ee0
[78250815.703870] PKRU: 55555554
[78250815.703871] Call Trace:
[78250815.703877]  thread_group_cputime_adjusted+0x4a/0x70
[78250815.703881]  do_task_stat+0x2ed/0xe00
[78250815.703885]  ? khugepaged_enter_vma_merge+0x12/0xd0
[78250815.703888]  proc_single_show+0x51/0xc0
[78250815.703892]  seq_read_iter+0x185/0x3c0
[78250815.703895]  seq_read+0x106/0x150
[78250815.703898]  vfs_read+0x98/0x180
[78250815.703900]  ksys_read+0x59/0xd0
[78250815.703904]  do_syscall_64+0x33/0x40
[78250815.703907]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[78250815.703910] RIP: 0033:0x318aeda360


It caused by a process with many threads running very long, and utime+stime overflowed 64bit, then cause the below div

mul_u64_u64_div_u64(0x69f98da9ba980c00, 0xfffd213aabd74626, 0x09e00900);

I see the comments of mul_u64_u64_div_u64() say:

Will generate an #DE when the result doesn't fit u64, could fix with an
__ex_table[] entry when it becomes an issu


Seem __ex_table[] entry for div does not work ?

Thanks

-Li