[Qemu-devel] [Bug 1679126] Re: null pointer access on migration resume of systemrescuecd boot menu with qxl-vga

[elmarco]

Interesting, the culprit is:

commit cd958edb1fae85d0c7d1e1acbff82d22724e8d64
Author: Marc-André Lureau <address@hidden>
Date:   Fri Aug 26 13:47:11 2016 +0400

    console: skip same-size resize
    
    virtio-gpu does a set-scanout at each frame (it might be a driver
    regression). qemu_console_resize() recreate a surface even if the size
    didn't change, and this shows up in profiling reports because the
    surface is cleared. With this patch, I get a +15-20% glmark2
    improvement.
    
    Signed-off-by: Marc-André Lureau <address@hidden>
    Message-id: address@hidden
    Signed-off-by: Gerd Hoffmann <address@hidden>

diff --git a/ui/console.c b/ui/console.c
index 3940762851..394786b3c7 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -2101,6 +2101,13 @@ void qemu_console_resize(QemuConsole *s, int width, int 
height)
     DisplaySurface *surface;
 
     assert(s->console_type == GRAPHIC_CONSOLE);
+
+    if (s->surface &&
+        pixman_image_get_width(s->surface->image) == width &&
+        pixman_image_get_height(s->surface->image) == height) {
+        return;
+    }

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https://bugs.launchpad.net/bugs/1679126

Title:
  null pointer access on migration resume of systemrescuecd boot menu
  with qxl-vga

Status in QEMU:
  Confirmed

Bug description:
  With qemu-2.8.0 up to 2.9.0-rc2 and git master (6954cdc), when
  resuming from a migration state file created from a VM suspended while
  showing the System Rescue CD 4.9.2 boot menu and using the QXL VGA
  device, I get a null point access in pixman_image_get_data called from
  qemu_spice_create_update (spice-display.c:215).  When I added
  assert(ssd->mirror != NULL) above that line, assert failed.  I don't
  get the crash when using standard VGA or cirrus-vga.  I am using
  gcc-4.9.3 on Gentoo x86_64 with Intel i7-4700HQ CPU and kernel:
  4.9.15-gentoo.

  Here is the valgrind trace from the git version:
  ==2634== Thread 1:
  ==2634== Invalid read of size 4
  ==3516==    at 0x65F3050: pixman_image_get_data (in 
/usr/lib64/libpixman-1.so.0.34.0)
  ==3516==    by 0x6F0CEB: qemu_spice_create_update (spice-display.c:215)
  ==3516==    by 0x6F1CC7: qemu_spice_display_refresh (spice-display.c:502)
  ==3516==    by 0x58CF77: display_refresh (qxl.c:1948)
  ==3516==    by 0x6E8084: do_safe_dpy_refresh (console.c:1591)
  ==3516==    by 0x6E80D5: dpy_refresh (console.c:1604)
  ==3516==    by 0x6E4508: gui_update (console.c:201)
  ==3516==    by 0x81898E: timerlist_run_timers (qemu-timer.c:536)
  ==3516==    by 0x8189D6: qemu_clock_run_timers (qemu-timer.c:547)
  ==3516==    by 0x818D98: qemu_clock_run_all_timers (qemu-timer.c:662)
  ==3516==    by 0x81952A: main_loop_wait (main-loop.c:514)
  ==3516==    by 0x4ADD29: main_loop (vl.c:1898)

  Minimal steps to reproduce:

  Compile (debug compile flags are just so valgrind works, the crash occurs 
with non-debug compile flags as well):
  CFLAGS="-g -O0" CXXFLAGS="-g -O0" ./configure 
--target-list=i386-softmmu,x86_64-softmmu
  ./configure
  make

  Start VM and leave it on the System Rescue CD graphical boot menu:
  x86_64-softmmu/qemu-system-x86_64 -nodefaults -machine pc -drive 
file=systemrescuecd-x86-4.9.2.iso,if=none,id=cdrom-cd,readonly=on -device 
ide-cd,bus=ide.0,drive=cdrom-cd,bootindex=1 -device qxl-vga -monitor 
unix:monitor.sock,server,nowait -display gtk

  Suspend VM and save state:
  socat - unix:monitor.sock
    stop
    migrate "exec:cat > vm.state"
    quit

  Attempt to resume VM (but this crashes):
  x86_64-softmmu/qemu-system-x86_64 -nodefaults -machine pc -drive 
file=systemrescuecd-x86-4.9.2.iso,if=none,id=cdrom-cd,readonly=on -device 
ide-cd,bus=ide.0,drive=cdrom-cd,bootindex=1 -device qxl-vga -monitor 
unix:monitor.sock,server,nowait -display gtk -incoming exec:"cat vm.state"

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