Re: [sched] 9ae606bc74: WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture]

[Oliver Sang]

hi Will,

On Mon, Jul 25, 2022 at 10:20:58AM +0100, Will Deacon wrote:
> 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@xxxxxxxxxxxxxxxxxxxx>
> > 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.

Thanks a lot for your information!
we will do some further tests to see if below part could impact x86.
will update you next week. thanks

@@ -3124,9 +3124,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)

                /* Look for allowed, online CPU in same node. */
                for_each_cpu(dest_cpu, nodemask) {
-                       if (!cpu_active(dest_cpu))
-                               continue;
-                       if (cpumask_test_cpu(dest_cpu, p->cpus_ptr))
+                       if (is_cpu_allowed(p, dest_cpu))
                                return dest_cpu;
                }
        }


> 
> Will