Re: [PATCH v2 3/3] console: make QMP/HMP screendump run in coroutine

[Gerd Hoffmann]

On Wed, Jan 20, 2021 at 06:29:41PM +0400, Marc-André Lureau wrote:
> Hi Gerd
> 
> On Wed, Jan 20, 2021 at 6:18 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
> >
> > On Tue, Oct 27, 2020 at 05:36:02PM +0400, marcandre.lureau@redhat.com wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > Thanks to the monitors' coroutine support (merge commit b7092cda1b3),
> > > the screendump handler can trigger a graphic_hw_update(), yield and let
> > > the main loop run until update is done. Then the handler is resumed, and
> > > ppm_save() will write the screen image to disk in the coroutine context.
> > >
> > > The IO is still blocking though, as the file is set blocking so far,
> > > this could be addressed by some future change (with other caveats).
> > >
> > > Related to:
> > > https://bugzilla.redhat.com/show_bug.cgi?id=1230527
> > >
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
> >
> > Hmm, just noticed that with this patch applied screendump hangs for vms
> > with "-device qxl" ("-device qxl-vga" works fine).
> >
> > Can you have a look?
> 
> Weird, I cannot reproduce. I tried this way:
> 
> $ qemu-system-x86_64 -m 4096 -enable-kvm -device qxl -qmp
> unix:/tmp/qmp.sock,server -snapshot rhel8

-vga none or -nodefaults is needed, otherwise you'll get both VGA and
qxl devices.

Using gtk ui, just saying "screendump /tmp/x" in the monitor tab.

> Can you also provide a backtrace?

Thread 9 (Thread 0x7fab97638640 (LWP 2822854) "pool-qemu"):
#0  0x00007fab9c8af30d in syscall () at /lib64/libc.so.6
#1  0x00007fab9db7f2ec in g_cond_wait_until () at /lib64/libglib-2.0.so.0
#2  0x00007fab9db033c1 in g_async_queue_pop_intern_unlocked () at 
/lib64/libglib-2.0.so.0
#3  0x00007fab9db03546 in g_async_queue_timeout_pop () at 
/lib64/libglib-2.0.so.0
#4  0x00007fab9db62ef9 in g_thread_pool_thread_proxy.lto_priv () at 
/lib64/libglib-2.0.so.0
#5  0x00007fab9db602b2 in g_thread_proxy () at /lib64/libglib-2.0.so.0
#6  0x00007fab9c9873f9 in start_thread () at /lib64/libpthread.so.0
#7  0x00007fab9c8b4903 in clone () at /lib64/libc.so.6

Thread 8 (Thread 0x7fab37dff640 (LWP 2822804) "SPICE Worker"):
#0  0x00007fab9c8a980f in poll () at /lib64/libc.so.6
#1  0x00007fab9db846f6 in g_main_context_iterate.constprop () at 
/lib64/libglib-2.0.so.0
#2  0x00007fab9db32033 in g_main_loop_run () at /lib64/libglib-2.0.so.0
#3  0x00007fab9de87c66 in red_worker_main.lto_priv () at 
/lib64/libspice-server.so.1
#4  0x00007fab9c9873f9 in start_thread () at /lib64/libpthread.so.0
#5  0x00007fab9c8b4903 in clone () at /lib64/libc.so.6

Thread 7 (Thread 0x7fab95a8b640 (LWP 2822803) "qemu-system-x86"):
#0  0x00007fab9c990ea0 in __lll_lock_wait () at /lib64/libpthread.so.0
#1  0x00007fab9c989763 in pthread_mutex_lock () at /lib64/libpthread.so.0
#2  0x000055f3f9c1c7e9 in qemu_mutex_lock_impl ()
#3  0x000055f3f9a1357f in qemu_mutex_lock_iothread_impl ()
#4  0x000055f3f9a52c86 in mttcg_cpu_thread_fn ()
#5  0x000055f3f9c1c689 in qemu_thread_start ()
#6  0x00007fab9c9873f9 in start_thread () at /lib64/libpthread.so.0
#7  0x00007fab9c8b4903 in clone () at /lib64/libc.so.6

Thread 6 (Thread 0x7fab96596640 (LWP 2822802) "dconf worker"):
#0  0x00007fab9c8a980f in poll () at /lib64/libc.so.6
#1  0x00007fab9db846f6 in g_main_context_iterate.constprop () at 
/lib64/libglib-2.0.so.0
#2  0x00007fab9db2fd43 in g_main_context_iteration () at /lib64/libglib-2.0.so.0
#3  0x00007fab9e0ac64d in dconf_gdbus_worker_thread () at 
/usr/lib64/gio/modules/libdconfsettings.so
#4  0x00007fab9db602b2 in g_thread_proxy () at /lib64/libglib-2.0.so.0
#5  0x00007fab9c9873f9 in start_thread () at /lib64/libpthread.so.0
#6  0x00007fab9c8b4903 in clone () at /lib64/libc.so.6

Thread 5 (Thread 0x7fab96d97640 (LWP 2822801) "gdbus"):
#0  0x00007fab9c8a980f in poll () at /lib64/libc.so.6
#1  0x00007fab9db846f6 in g_main_context_iterate.constprop () at 
/lib64/libglib-2.0.so.0
#2  0x00007fab9db32033 in g_main_loop_run () at /lib64/libglib-2.0.so.0
#3  0x00007fab9da21d1a in gdbus_shared_thread_func.lto_priv () at 
/lib64/libgio-2.0.so.0
#4  0x00007fab9db602b2 in g_thread_proxy () at /lib64/libglib-2.0.so.0
#5  0x00007fab9c9873f9 in start_thread () at /lib64/libpthread.so.0
#6  0x00007fab9c8b4903 in clone () at /lib64/libc.so.6

Thread 3 (Thread 0x7fab97e39640 (LWP 2822799) "gmain"):
#0  0x00007fab9c8a980f in poll () at /lib64/libc.so.6
#1  0x00007fab9db846f6 in g_main_context_iterate.constprop () at 
/lib64/libglib-2.0.so.0
#2  0x00007fab9db2fd43 in g_main_context_iteration () at /lib64/libglib-2.0.so.0
#3  0x00007fab9db31961 in glib_worker_main () at /lib64/libglib-2.0.so.0
#4  0x00007fab9db602b2 in g_thread_proxy () at /lib64/libglib-2.0.so.0
#5  0x00007fab9c9873f9 in start_thread () at /lib64/libpthread.so.0
#6  0x00007fab9c8b4903 in clone () at /lib64/libc.so.6

Thread 2 (Thread 0x7fab9873b640 (LWP 2822798) "qemu-system-x86"):
#0  0x00007fab9c8af30d in syscall () at /lib64/libc.so.6
#1  0x000055f3f9c1d53a in qemu_event_wait ()
#2  0x000055f3f9c17c9a in call_rcu_thread ()
#3  0x000055f3f9c1c689 in qemu_thread_start ()
#4  0x00007fab9c9873f9 in start_thread () at /lib64/libpthread.so.0
#5  0x00007fab9c8b4903 in clone () at /lib64/libc.so.6

Thread 1 (Thread 0x7fab988e4440 (LWP 2822797) "qemu-system-x86"):
#0  0x00007fab9c8a990e in ppoll () at /lib64/libc.so.6
#1  0x000055f3f9c33dd5 in fdmon_poll_wait ()
#2  0x000055f3f9c26c6a in aio_poll ()
#3  0x000055f3f99552a5 in handle_hmp_command ()
#4  0x000055f3f99553cd in monitor_command_cb ()
#5  0x000055f3f9c29a37 in readline_handle_byte ()
#6  0x000055f3f995541b in monitor_read ()
#7  0x000055f3f992373c in gd_vc_in ()
#8  0x00007fab9d84e22d in _vte_marshal_VOID__STRING_UINTv () at 
/lib64/libvte-2.91.so.0
#9  0x00007fab9d8e9080 in g_signal_emit_valist () at /lib64/libgobject-2.0.so.0
#10 0x00007fab9d8e91a3 in g_signal_emit () at /lib64/libgobject-2.0.so.0
#11 0x00007fab9d858a7e in 
vte::terminal::Terminal::emit_commit(std::basic_string_view<char, 
std::char_traits<char> > const&) () at /lib64/libvte-2.91.so.0
#12 0x00007fab9d85cf1d in 
vte::terminal::Terminal::send_child(std::basic_string_view<char, 
std::char_traits<char> > const&) () at /lib64/libvte-2.91.so.0
#13 0x00007fab9d8715bc in vte_terminal_key_press(_GtkWidget*, _GdkEventKey*) () 
at /lib64/libvte-2.91.so.0
#14 0x00007fab9d47eccc in _gtk_marshal_BOOLEAN__BOXEDv () at 
/lib64/libgtk-3.so.0
#15 0x00007fab9d8e869a in g_signal_emit_valist () at /lib64/libgobject-2.0.so.0
#16 0x00007fab9d8e91a3 in g_signal_emit () at /lib64/libgobject-2.0.so.0
#17 0x00007fab9d441bb4 in gtk_widget_event_internal.part.0.lto_priv () at 
/lib64/libgtk-3.so.0
#18 0x00007fab9d45029b in gtk_window_propagate_key_event () at 
/lib64/libgtk-3.so.0
#19 0x00007fab9d453283 in gtk_window_key_press_event.lto_priv () at 
/lib64/libgtk-3.so.0
#20 0x00007fab9d47eccc in _gtk_marshal_BOOLEAN__BOXEDv () at 
/lib64/libgtk-3.so.0
#21 0x00007fab9d8e9080 in g_signal_emit_valist () at /lib64/libgobject-2.0.so.0
#22 0x00007fab9d8e91a3 in g_signal_emit () at /lib64/libgobject-2.0.so.0
#23 0x00007fab9d441bb4 in gtk_widget_event_internal.part.0.lto_priv () at 
/lib64/libgtk-3.so.0
#24 0x00007fab9d2e000f in propagate_event.lto_priv () at /lib64/libgtk-3.so.0
#25 0x00007fab9d2e1223 in gtk_main_do_event () at /lib64/libgtk-3.so.0
#26 0x00007fab9cfbb633 in _gdk_event_emit () at /lib64/libgdk-3.so.0
#27 0x00007fab9d022ba6 in gdk_event_source_dispatch.lto_priv () at 
/lib64/libgdk-3.so.0
#28 0x00007fab9db3296f in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
#29 0x000055f3f9c24f58 in main_loop_wait ()
#30 0x000055f3f9a564b1 in qemu_main_loop ()
#31 0x000055f3f97609ee in main ()

take care,
  Gerd