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Re: [Qemu-devel] [PATCH] secondary-vga: unregister vram on unplug.
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH] secondary-vga: unregister vram on unplug. |
Date: |
Tue, 7 Aug 2018 16:09:35 +0100 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
* Peter Maydell (address@hidden) wrote:
> On 7 August 2018 at 15:57, Dr. David Alan Gilbert <address@hidden> wrote:
> > * Gerd Hoffmann (address@hidden) wrote:
> >> On Fri, Jul 20, 2018 at 10:19:48AM +0200, address@hidden wrote:
> >> > From: "Remy Noel" <address@hidden>
> >> >
> >> > When removing a secondary-vga device and then adding it back (or adding
> >> > an other one), qemu aborts with:
> >> > "RAMBlock "0000:00:02.0/vga.vram" already registered, abort!".
> >> >
> >> > It is caused by the vram staying registered, preventing vga replugging.
> >>
> >> David? Does that look ok?
> >>
> >> This balances the
> >>
> >> vmstate_register_ram(&s->vram, s->global_vmstate ? NULL :
> >> DEVICE(obj));
> >>
> >> call in vga_common_init(). I'm wondering whenever the manual cleanup is
> >> actually needed in case owner is not NULL?
> >
> > I can't see anyone who is calling unregister_ram or the functions it
> > calls as part of generic device cleanup, so I think it IS needed
> > to manually do it.
> >
> > Which is a bit worrying since we have vastly more register's than
> > unregister's.
>
> Paolo suggested in an email last month that vmstate_unregister_ram()
> should simply not exist, because it doesn't actually do anything useful:
> https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg01125.html
>
> (ie it was added in the first place because we'd ended up with
> two identically named ramblocks, but that only happened because
> a reference-counting bug meant we hadn't deleted the first one
> properly before creating the second.)
>
> So I think that the bug reported in this thread is similar:
> the problem is not that we're not calling vmstate_unregister_ram(),
> but that when the first instance of secondary-vga is removed
> it is not correctly destroying the ramblock.
Ah yes that makes more sense; I remember there was another similar bug
where a device screwed up and didn't delete it's RAM causing similar
problems.
Dave
> thanks
> -- PMM
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK