Re: [PATCH v7 1/2] memory: Update inline documentation

[Peter Maydell]

On Tue, 14 Jan 2025 at 17:02, Peter Xu <peterx@redhat.com> wrote:
>
> On Tue, Jan 14, 2025 at 05:43:09PM +0900, Akihiko Odaki wrote:
> > memory_region_finalize() is not a function to tell the owner is leaving, but
> > the memory region itself is being destroyed.
>
> It is when the lifecycle of the MR is the same as the owner.  That holds
> true I suppose if without this patch, and that's why I don't prefer this
> patch because it makes that part more complicated.
>
> > It should not happen when a container is still referencing it. That is
> > also why it has memory_region_ref(subregion) in
> > memory_region_update_container_subregions() and assert(!mr->container) in
> > memory_region_finalize().
>
> Again, the line I added was sololy for what you said "automation" elsewhere
> and only should work within MR-links within the same owner.  Otherwise
> anyone referencing the MR would hold the owner ref then this finalize()
> will never happen.
>
> Now, if I could go back to your original purpose of this work, quotting
> from your cover letter:
>
> > I saw various sanitizer errors when running check-qtest-ppc64. While
> > I could just turn off sanitizers, I decided to tackle them this time.
> >
> > Unfortunately, GLib versions older than 2.81.0 do not free test data in
> > some cases so some sanitizer errors remain. All sanitizer errors will be
> > gone with this patch series combined with the following change for GLib:
> > https://gitlab.gnome.org/GNOME/glib/-/merge_requests/4120
>
> Is check-qtest-ppc64 the only one that will trigger this issue?  Does it
> mean that most of the devices will do proper removal of device-owned
> subregions (hence, not prone to circular reference of owner refcount)
> except some devices in ppc64?

There's at least one test in the arm qtests that will hit this.
I suspect that you'll find that most architectures except x86
(where we don't have models of complex SoCs and the few
machines we do have tend to be old code that is less QOMified)
will hit similar issues. I think there's a general issue here,
this isn't just "some particular ppc device is wrongly coded".

-- PMM