linux-kernel - Re: [PATCH v2] PCI: Reinstate "PCI: Coalesce host bridge contiguous apertures"

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Date:   Wed, 13 Jul 2022 11:36:41 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Guenter Roeck <linux@...ck-us.net>,
        "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: Reinstate "PCI: Coalesce host bridge contiguous apertures"

Hi Johannes,

On Wed, Nov 17, 2021 at 6:41 PM Johannes Berg <johannes@...solutions.net> wrote:
> So this patch landed now ... :)
>
> > +     /* Coalesce contiguous windows */
> > +     resource_list_for_each_entry_safe(window, n, &resources) {
> > +             if (list_is_last(&window->node, &resources))
> > +                     break;
> > +
> > +             next = list_next_entry(window, node);
> > +             offset = window->offset;
> > +             res = window->res;
> > +             next_offset = next->offset;
> > +             next_res = next->res;
> > +
> > +             if (res->flags != next_res->flags || offset != next_offset)
> > +                     continue;
> > +
> > +             if (res->end + 1 == next_res->start) {
> > +                     next_res->start = res->start;
> > +                     res->flags = res->start = res->end = 0;
> > +             }
> > +     }
> >
>
> Maybe this was already a problem before - but I had a stupid thing in
> arch/um/drivers/virt-pci.c (busn_resource has start == end == 0), and
> your changes here caused that resource to be dropped off the list.
>
> Now this wouldn't be a problem, but we add it using pci_add_resource()
> and then that does a memory allocation, but you don't free it here? I'm
> not sure it'd even be safe to free it here and I'll just set
> busn_resource to have end==1 instead (it's all kind of virtual).
>
> But I still wanted to ask if this might be a problem here for others.

Yes it is.  I've sent a fix
https://lore.kernel.org/r/9c41a4372b27420c732ff5599d823e363de00c6d.1657704829.git.geert+renesas@glider.be

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds