Comment by gsg

You can easily see by searching for 'kmalloc' (or 'malloc') at https://github.com/torvalds/linux/blob/master/include/linux/... that it does no such thing.

Here's the logic for adding a list node:

    /*
     * Insert a new entry between two known consecutive entries.
     *
     * This is only for internal list manipulation where we know
     * the prev/next entries already!
     */
    static inline void __list_add(struct list_head *new,
                                  struct list_head *prev,
                                  struct list_head *next)
    {
            if (!__list_add_valid(new, prev, next))
                    return;

            next->prev = new;
            new->next = next;
            new->prev = prev;
            WRITE_ONCE(prev->next, new);
    }

No allocation, just mutating some fields in preexisting list_head structures. Those are by convention stored as a field in whatever struct needs to be kept in the list, which is what 'intrusive' means.