linux-kernel - Re: [PATCH v2] sched/core: Use empty mask to reset cpumasks in sched

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Date:   Thu, 3 Aug 2023 12:03:00 -0400
From:   Waiman Long <longman@...hat.com>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     oe-lkp@...ts.linux.dev, lkp@...el.com,
        linux-kernel@...r.kernel.org, aubrey.li@...ux.intel.com,
        yu.c.chen@...el.com, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Phil Auld <pauld@...hat.com>,
        Brent Rowsell <browsell@...hat.com>,
        Peter Hunt <pehunt@...hat.com>
Subject: Re: [PATCH v2] sched/core: Use empty mask to reset cpumasks in
 sched_setaffinity()


On 7/25/23 09:07, kernel test robot wrote:
>
> Hello,
>
> kernel test robot noticed "kernel-selftests.vDSO.vdso_test_correctness.fail" on:
>
> commit: 8bd21fae1e37284f0f78fa42fb4d20a6cadfa68a ("[PATCH v2] sched/core: Use empty mask to reset cpumasks in sched_setaffinity()")
> url: https://github.com/intel-lab-lkp/linux/commits/Waiman-Long/sched-core-Use-empty-mask-to-reset-cpumasks-in-sched_setaffinity/20230718-194823
> base: https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git 2ae2fb98b77339277a2c2f18dfec605dfd8dd321
> patch link: https://lore.kernel.org/all/20230717180243.3607603-1-longman@redhat.com/
> patch subject: [PATCH v2] sched/core: Use empty mask to reset cpumasks in sched_setaffinity()
>
> in testcase: kernel-selftests
> version: kernel-selftests-x86_64-60acb023-1_20230329
> with following parameters:
>
> 	group: group-03
>
>
>
> compiler: gcc-12
> test machine: 36 threads 1 sockets Intel(R) Core(TM) i9-10980XE CPU @ 3.00GHz (Cascade Lake) with 32G memory
>
> (please refer to attached dmesg/kmsg for entire log/backtrace)
> # [OK]	CPU 34: syscall: cpu 34, node 0 vdso: cpu 34, node 0 vsyscall: cpu 34, node 0
> # [OK]	CPU 35: syscall: cpu 35, node 0 vdso: cpu 35, node 0 vsyscall: cpu 35, node 0
> # [FAIL]	CPU 36: syscall: cpu 35, node 0 vdso: cpu 35, node 0 vsyscall: cpu 35, node 0
> not ok 6 selftests: vDSO: vdso_test_correctness # exit=1

I have figured out what this fail. The vdso_test_correctness.c test 
calls sched_setaffinity() from cpu 0 and up until it hits an error 
return. There are 36 CPUs in the test system and once the CPU number hit 
36, the cpumask_empty() test in sched_setaffinity() returns true causing 
a non-error return.

It seems like I need to always return an error code to not break 
existing test program, but perhaps with a different error code to 
indicate some action is done.

Cheers,
Longman