In the Linux kernel, the following vulnerability has been resolved:
sched: Fix yet more sched_fork() races
Where commit 4ef0c5c6b5ba ("kernel/sched: Fix schedfork() access an invalid schedtask_group") fixed a fork race vs cgroup, it opened up a race vs syscalls by not placing the task on the runqueue before it gets exposed through the pidhash.
Commit 13765de8148f ("sched/fair: Fix fault in reweight_entity") is trying to fix a single instance of this, instead fix the whole class of issues, effectively reverting this commit.