linux-kernel - Re: [sched] 9ae606bc74: WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats

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Message-ID: <20220725092057.GB20370@willie-the-truck>
Date:   Mon, 25 Jul 2022 10:20:58 +0100
From:   Will Deacon <will@...nel.org>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <Valentin.Schneider@....com>,
        Quentin Perret <qperret@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        lkp@...el.com, aubrey.li@...ux.intel.com, yu.c.chen@...el.com
Subject: Re: [sched]  9ae606bc74:
 WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture]

On Mon, Jul 25, 2022 at 04:12:57PM +0800, kernel test robot wrote:
> 
> 
> Greeting,
> 
> FYI, we noticed the following commit (built with clang-15):
> 
> commit: 9ae606bc74dd0e58d4de894e3c5cbb9d45599267 ("sched: Introduce task_cpu_possible_mask() to limit fallback rq selection")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: rcutorture
> version: 
> with following parameters:
> 
> 	runtime: 300s
> 	test: cpuhotplug
> 	torture_type: trivial
> 
> test-description: rcutorture is rcutorture kernel module load/unload test.
> test-url: https://www.kernel.org/doc/Documentation/RCU/torture.txt
> 
> 
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> 
> 
> +-------------------------------------------------------------------------+------------+------------+
> |                                                                         | 304000390f | 9ae606bc74 |
> +-------------------------------------------------------------------------+------------+------------+
> | WARNING:at_kernel/rcu/rcutorture.c:#synchronize_rcu_trivial[rcutorture] | 120        | 120        |
> | RIP:synchronize_rcu_trivial[rcutorture]                                 | 120        | 120        |
> | WARNING:at_kernel/rcu/update.c:#rcutorture_sched_setaffinity            | 120        | 120        |
> | RIP:rcutorture_sched_setaffinity                                        | 120        | 120        |
> | WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture] | 0          | 36         |
> | RIP:rcu_torture_stats_print[rcutorture]                                 | 0          | 36         |
> +-------------------------------------------------------------------------+------------+------------+
> 
> 
> please be noted, since 9ae606bc74 is kind of old, we also tested on a latest
> mainline commit:
> commit 515f71412bb73ebd7f41f90e1684fc80b8730789
> Merge: 301c8949322fe cf5029d5dd7cb
> Author: Linus Torvalds <torvalds@...ux-foundation.org>
> Date:   Sat Jul 23 10:22:26 2022 -0700
> 
> and confirmed the
>    WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture]
> still exists.

I'm not convinced by the bisection -- that commit should't have any effect
on x86.

Will