On 03/04/24 10:47, Waiman Long wrote: > On 4/3/24 10:26, Valentin Schneider wrote: >> IIUC that was Thomas' suggestion [1], but I can't tell yet how bad it would >> be to change cgroup_lock() to also do a cpus_read_lock(). > > Changing the locking order is certainly doable. I have taken a cursory > look at it and at least the following files need to be changed: > > kernel/bpf/cgroup.c > kernel/cgroup/cgroup.c > kernel/cgroup/legacy_freezer.c > mm/memcontrol.c > > That requires a lot more testing to make sure that there won't be a > regression. Given that the call to cgroup_transfer_tasks() should be > rare these days as it will only apply in the case of cgroup v1 under > certain condtion, I am not sure this requirement justifies making such > extensive changes. So I kind of defer it until we reach a consensus that > it is the right thing to do. > Yeah if we can avoid it initially I'd be up for it. Just one thing that came to mind - there's no flushing of the cpuset_migrate_tasks_workfn() work, so the scheduler might move tasks itself before the cpuset does via: balance_push() ->__balance_push_cpu_stop() -> select_fallback_rq() But, given the current placement of cpuset_wait_for_hotplug(), I believe that's something we can already have, so we should be good. > Cheers, > Longman
