On 3/18/26 8:53 AM, Paul E. McKenney wrote:
Hello!
Running rcutorture on v7.0-rc3 results in spurious CPU-hotplug failures,
most frequently on the TREE03 scenario, which suffers about ten such
failures per hundred hours of test time. Repeat-by is as follows:
tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 80 --duration 100h --configs
"100*TREE03" --trust-make
Though a faster repeat-by instead uses kvm-remote.sh and lots of systems.
Bisection converges here:
6df415aa46ec ("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to
workqueue")
Reverting this commit gets rid of the spurious CPU-hotplug failures.
Of course, this also gets rid of some ability to do dynamic nohz_full
processing.
Now, the problem might be that the workqueue handler might still be
in flight by the time that rcutorture fired up the next CPU-hotplug
operation, especially given that the TREE03 scenario only waits 200
milliseconds between these operations. This suggests waiting for this
handler before ending each CPU-hotplug operation. And the crude patch
below does make the problem go away.
This alleged fix is quite heavy-handed, and also fragile in that if
hk_sd_workfn() uses a different workqueue, this breaks. It might be
better to call into the cgroups/cpusets code and to use flush_work()
to wait only on hk_sd_workfn() and nothing else. But it seemed best to
keep things trivial to start with.
Either way, please consider the patch below to be part of this bug report
rather than a proper fix.
Thoughts?
Thanx, Paul
There is a fix commit ca174c705db5 ("cgroup/cpuset: Call
rebuild_sched_domains() directly in hotplug") in rc4 that may help. Could
you try out the rc4 kernel to see if that can resolve the problem that
you have?
Thanks,
Longman
