linux-kernel - Re: [LKP] Re: [rcuperf] 4e88ec4a9e: UBSAN:division-overflow_in

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Date:   Wed, 2 Sep 2020 12:34:59 +0800
From:   "Chen, Rong A" <rong.a.chen@...el.com>
To:     paulmck@...nel.org
Cc:     kernel test robot <lkp@...el.com>, Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org
Subject: Re: [LKP] Re: [rcuperf] 4e88ec4a9e:
 UBSAN:division-overflow_in_arch/x86/include/asm/div64.h



On 9/2/2020 12:27 AM, Paul E. McKenney wrote:
> On Tue, Sep 01, 2020 at 03:03:28PM +0800, Rong Chen wrote:
>>
>> On 8/31/20 11:50 PM, Paul E. McKenney wrote:
>>> On Mon, Aug 31, 2020 at 08:01:22PM +0800, kernel test robot wrote:
>>>> Greeting,
>>>>
>>>> FYI, we noticed the following commit (built with gcc-9):
>>>>
>>>> commit: 4e88ec4a9eb17527e640b063f79e5b875733eb53 ("rcuperf: Change rcuperf to rcuscale")
>>>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>>>>
>>>>
>>>> in testcase: trinity
>>>> with following parameters:
>>>>
>>>> 	runtime: 300s
>>>>
>>>> test-description: Trinity is a linux system call fuzz tester.
>>>> test-url: http://codemonkey.org.uk/projects/trinity/
>>>>
>>>>
>>>> on test machine: qemu-system-i386 -enable-kvm -cpu SandyBridge -smp 2 -m 8G
>>>>
>>>> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>>>>
>>>>
>>>> +---------------------------------------------------------+------------+------------+
>>>> |                                                         | 65bd77f554 | 4e88ec4a9e |
>>>> +---------------------------------------------------------+------------+------------+
>>>> | boot_successes                                          | 13         | 0          |
>>>> | boot_failures                                           | 0          | 14         |
>>>> | UBSAN:division-overflow_in_arch/x86/include/asm/div64.h | 0          | 14         |
>>>> | error:#[##]                                             | 0          | 14         |
>>>> | EIP:main_func.cold                                      | 0          | 14         |
>>>> | Kernel_panic-not_syncing:Fatal_exception                | 0          | 14         |
>>>> +---------------------------------------------------------+------------+------------+
>>>>
>>>>
>>>> If you fix the issue, kindly add following tag
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>> Does the patch below fix this for you?
>> Yes, this patch can fix the issue, and nreaders was adjusted to 1:
>>
>> [    5.953645] The force parameter has not been set to 1. The Iris poweroff
>> handler will not be installed.
>> [   12.546587] rcu-ref-scale: --- Start of test:  verbose=0 shutdown=1
>> holdoff=10 loops=10000 nreaders=-1 nruns=30 readdelay=0
>> [   12.561495] ------------[ cut here ]------------
>> [   12.562016] ref_scale_init: nreaders = 0, adjusted to 1
>> [   12.562601] WARNING: CPU: 0 PID: 1 at kernel/rcu/refscale.c:684
>> ref_scale_init+0x653/0x80
> Thank you!  May I add your Tested-by?
Yes,  please, it's my pleasure.

Best Regards,
Rong Chen

>
> 							Thanx, Paul
>
>> Best Regards,
>> Rong Chen
>>
>>> 							Thanx, Paul
>>>
>>> ------------------------------------------------------------------------
>>>
>>> commit d301e320e952e2e604d83d9540e52510b0eb3d94
>>> Author: Paul E. McKenney <paulmck@...nel.org>
>>> Date:   Thu Aug 27 09:58:19 2020 -0700
>>>
>>>       refscale: Bounds-check module parameters
>>>       The default value for refscale.nreaders is -1, which results in the code
>>>       setting the value to three-quarters of the number of CPUs.  On single-CPU
>>>       systems, this results in three-quarters of the value one, which the C
>>>       language's integer arithmetic rounds to zero.  This in turn results in
>>>       a divide-by-zero error.
>>>       This commit therefore adds bounds checking to the refscale module
>>>       parameters, so that if they are less than one, they are set to the
>>>       value one.
>>>       Reported-by: kernel test robot <lkp@...el.com>
>>>       Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
>>>
>>> diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
>>> index 952595c..fb5f20d 100644
>>> --- a/kernel/rcu/refscale.c
>>> +++ b/kernel/rcu/refscale.c
>>> @@ -681,6 +681,12 @@ ref_scale_init(void)
>>>    	// Reader tasks (default to ~75% of online CPUs).
>>>    	if (nreaders < 0)
>>>    		nreaders = (num_online_cpus() >> 1) + (num_online_cpus() >> 2);
>>> +	if (WARN_ONCE(loops <= 0, "%s: loops = %ld, adjusted to 1\n", __func__, loops))
>>> +		loops = 1;
>>> +	if (WARN_ONCE(nreaders <= 0, "%s: nreaders = %d, adjusted to 1\n", __func__, nreaders))
>>> +		nreaders = 1;
>>> +	if (WARN_ONCE(nruns <= 0, "%s: nruns = %d, adjusted to 1\n", __func__, nruns))
>>> +		nruns = 1;
>>>    	reader_tasks = kcalloc(nreaders, sizeof(reader_tasks[0]),
>>>    			       GFP_KERNEL);
>>>    	if (!reader_tasks) {
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