On Tue, Mar 08, 2022 at 04:12:32PM +0100, Michal Koutný wrote:
Hello.
On Mon, Feb 28, 2022 at 06:24:07PM +0100, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
[...] cpuset_attach() cpu hotplug --------------------------- ---------------------- down_write(cpuset_rwsem) guarantee_online_cpus() // (load cpus_attach) sched_cpu_deactivate set_cpu_active() // will change cpu_active_mask set_cpus_allowed_ptr(cpus_attach) __set_cpus_allowed_ptr_locked() // (if the intersection of cpus_attach and cpu_active_mask is empty, will return -EINVAL) up_write(cpuset_rwsem) [...] --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1528,6 +1528,7 @@ static void cpuset_attach(struct cgroup_ cgroup_taskset_first(tset, &css); cs = css_cs(css);
- cpus_read_lock(); mutex_lock(&cpuset_mutex);
This backport (and possible older kernels) looks suspicious since it comes before commit d74b27d63a8b ("cgroup/cpuset: Change cpuset_rwsem and hotplug lock order") v5.4-rc1~176^2~30 when the locking order was: cpuset lock, cpus lock.
At the same time it also comes before commit 710da3c8ea7d ("sched/core: Prevent race condition between cpuset and __sched_setscheduler()") v5.4-rc1~176^2~27 when neither __sched_setscheduler() cared and this race is similar. (The swapped locking may still conflict with rebuild_sched_domains() before d74b27d63a8b.)
Thanks for noticing this. What do you recommend to do to resolve this?
thanks,
greg k-h