Re: Resend [PATCH] kernel/resource.c: invalidate parent when freed resource has childs

[Linus Torvalds]

On Fri, Aug 9, 2019 at 3:38 PM Wei Yang <richard.weiyang@xxxxxxxxx> wrote:
>
> In theory, child may have siblings. Would it be possible to have several
> devices under xhci-hcd?

I'm less interested in the xhci-hcd case - which I certainly *hope* is
fixed already? - than in "if this happens somewhere else".

So if we do want to remove the parent (which may be a good idea with a
warning), and want to make sure that the children are really removed
from the resource hierarchy, we should do somethiing like

  static bool detach_children(struct resource *res)
  {
        res = res->child;
        if (!res)
                return false;
        do {
                res->parent = NULL;
                res = res->sibling;
        } while (res);
        return true;
  }

and then we could write the __release_region() warning as

        /* You should not release a resource that has children */
        WARN_ON_ONCE(detach_children(res));

or something?

NOTE! The above is entirely untested, and written purely in my mail
reader. It might be seriously buggy, including not compiling, or doing
odd things. See it more as a "maybe something like this" code snippet
example than any kind of final form.

               Linus