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SubjectRe: [LKP] Re: [rcuperf] 4e88ec4a9e: UBSAN:division-overflow_in_arch/x86/include/asm/div64.h
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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@intel.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

Best Regards,
Rong Chen

>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit d301e320e952e2e604d83d9540e52510b0eb3d94
> Author: Paul E. McKenney <paulmck@kernel.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@intel.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.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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