[Bug 1882817] [NEW] Segfault in audio_pcm_sw_write with audio over VNC

* [Bug 1882817] [NEW] Segfault in audio_pcm_sw_write with audio over VNC
@ 2020-06-09 17:10 Artyom
  2020-06-09 18:00 ` Philippe Mathieu-Daudé
                   ` (4 more replies)
  0 siblings, 5 replies; 7+ messages in thread
From: Artyom @ 2020-06-09 17:10 UTC (permalink / raw)
  To: qemu-devel

Public bug reported:

QEMU 5.0.0, built with ./configure --target-list=x86_64-softmmu
--enable-debug --disable-strip --disable-docs --disable-sdl

Running on a headless host (Ryzen 3600), Arch Linux, 64bit latest.
Guest is also Arch Linux, 64bit.

Started with qemu-system-x86_64 -vnc 0.0.0.0:0 -enable-kvm -m 4096 -cpu host -smp cores=2,threads=1,sockets=1 -machine q35 -vga std -device
 ich9-ahci,id=ahci -drive file=vm0.qcow2,format=qcow2,if=none,id=dsk0 -device ide-hd,drive=dsk0,bus=ahci.0 -soundhw hda

So, a headless VM is running on a server and is being connected to over
VNC. The virtual sound card is detected and speaker test is running
inside the VM. So far so good.

Then, i tell the VNC client to enable audio (QEMU Audio Client Message,
255,1,0). QEMU responds with a "stream is about to start" message (QEMU
Audio Server Message, 255,1,1) and then promptly crashes without sending
anything else.

Running it in GDB produces a crash at audio/audio.c:739

Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
audio_pcm_sw_write (sw=0x5555575bbf30, buf=0x0, size=1628) at audio/audio.c:739
739             if (!sw->hw->pcm_ops->volume_out) {

The exact sequence of events does not matter - i can enable sound before
playing anything, and then it would say nothing and keep working, but
crash with the same message once anything sound-playing is launched in
the VM.

Using different soundhw or adding various audiodev options does not seem
to affect anything.

I can't quite figure out if the QEMU Audio VNC extension is supposed to
work at all or not, but it would be handy to me if it is.

** Affects: qemu
     Importance: Undecided
         Status: New

-- 
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https://bugs.launchpad.net/bugs/1882817

Title:
  Segfault in audio_pcm_sw_write with audio over VNC

Status in QEMU:
  New

Bug description:
  QEMU 5.0.0, built with ./configure --target-list=x86_64-softmmu
  --enable-debug --disable-strip --disable-docs --disable-sdl

  Running on a headless host (Ryzen 3600), Arch Linux, 64bit latest.
  Guest is also Arch Linux, 64bit.

  Started with qemu-system-x86_64 -vnc 0.0.0.0:0 -enable-kvm -m 4096 -cpu host -smp cores=2,threads=1,sockets=1 -machine q35 -vga std -device
   ich9-ahci,id=ahci -drive file=vm0.qcow2,format=qcow2,if=none,id=dsk0 -device ide-hd,drive=dsk0,bus=ahci.0 -soundhw hda

  So, a headless VM is running on a server and is being connected to
  over VNC. The virtual sound card is detected and speaker test is
  running inside the VM. So far so good.

  Then, i tell the VNC client to enable audio (QEMU Audio Client
  Message, 255,1,0). QEMU responds with a "stream is about to start"
  message (QEMU Audio Server Message, 255,1,1) and then promptly crashes
  without sending anything else.

  Running it in GDB produces a crash at audio/audio.c:739

  Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
  audio_pcm_sw_write (sw=0x5555575bbf30, buf=0x0, size=1628) at audio/audio.c:739
  739             if (!sw->hw->pcm_ops->volume_out) {

  The exact sequence of events does not matter - i can enable sound
  before playing anything, and then it would say nothing and keep
  working, but crash with the same message once anything sound-playing
  is launched in the VM.

  Using different soundhw or adding various audiodev options does not
  seem to affect anything.

  I can't quite figure out if the QEMU Audio VNC extension is supposed
  to work at all or not, but it would be handy to me if it is.

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