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Date: Tue, 18 Oct 2011 18:40:34 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2] Move graphic-related coalesced MMIO
 flushes to affected device models
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, qemu-devel <qemu-devel@nongnu.org>, David Gibson <david@gibson.dropbear.id.au>

On 10/18/2011 04:30 PM, Avi Kivity wrote:
> This takes a while to reproduce, let me talk to gdb for a bit.
>

a vcpu exit causes kvm_flush_coalesced_mmio_buffer() to run, which does
a bitblt, which is cirrus_do_copy(), which goes to vga_hw_update, which
does vga_update_display(), which calls
qemu_flush_coalesced_mmio_buffer(), which is not reentrant.

It's easy to make qemu_flush_coalesced_mmio_buffer reentrant:

  if (s->coalesced_flush_in_progress) {
      return;
  }

it isn't very pretty and is also a lie.  Other ideas?

I'll probably commit this soon to avoid the regression, to be replaced
by a better fix when we find it.

-- 
error compiling committee.c: too many arguments to function