Wow, that 2021 patch is amazing. They address the issue by adding this code:

    + spin_lock(&unix_gc_lock);
    + spin_unlock(&unix_gc_lock);

So they acquire+release a lock without doing anything in between, sort of as a way to introduce a barrier.

I have a vague feeling that if something like this is necessary, there is something odd about the locking model of that code in general. It most likely shows that locking is used in a process centric way, as opposed to data centric.