[Bug 2043517] Re: gnome-shell on non-active VT busy-loops through libwayland-server.so (sometimes)

Fri Dec 13 12:42:33 UTC 2024

** Changed in: xwayland (Ubuntu)
   Importance: Undecided => Medium

** Changed in: xwayland (Ubuntu Jammy)
   Importance: Undecided => Medium

** Changed in: xwayland (Ubuntu Noble)
   Importance: Undecided => Medium

** Changed in: xwayland (Ubuntu Oracular)
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/2043517

Title:
  gnome-shell on non-active VT busy-loops through libwayland-server.so
  (sometimes)

Status in X.Org X server:
  Fix Released
Status in mutter package in Ubuntu:
  Won't Fix
Status in xwayland package in Ubuntu:
  In Progress
Status in mutter source package in Jammy:
  Won't Fix
Status in xwayland source package in Jammy:
  In Progress
Status in mutter source package in Noble:
  Won't Fix
Status in xwayland source package in Noble:
  In Progress
Status in mutter source package in Oracular:
  Won't Fix
Status in xwayland source package in Oracular:
  In Progress

Bug description:
  [ Impact ]

  gnome-shell running on an inactive VT will sometimes start using 100% CPU.
  When that happens, the Xwayland child process is seen using 40% CPU.

  [ Test Plan ]

  1. Log in to GNOME Wayland
  2. Open a terminal window
  3. Terminate Xwayland if it was automatically started:
     $ pkill -SIGTERM Xwayland
  4. Run the following command:
     $ sleep 5; xlsclients
  5. Within 5 seconds, switch TTY with Ctrl+Alt+F3
  6. Log-in to the terminal
  7. Run:
     $ top -p $(pidof gnome-shell)
  8. Verify that gnome-shell is using close to 0% CPU, for at least 5 seconds.
  9. Return to GNOME by switching TTY with Ctrl+Alt+F2
  10. Verify that the `xlsclients` command has terminated

  [ Where problems could occur ]

  Xwayland is used to run X11 applications in a Wayland desktop.
  If Xwayland is malfunctioning, you will notice by not being able to run X11 apps anymore.
  In a Wayland desktop those would typically be legacy electron-based or java-based apps.

  [ Original Bug Report ]

  I run several gnome sessions at once - different users on different
  Virtual Terminals.

  Sometimes, gnome-shell for a non-active VT starts using 100% CPU.  Or,
  actually 99% CPU because it's doing IPC as well.  And the
  corresponding XWayland uses 40% CPU.

  FWIW, sending SIGSTOP to either gnome-shell or XWayland stops the
  other one from busy-looping as well.

  If I switch back to the affected VT, it appears to function fine, but
  it is still using 100% + 40% CPU.

  Version numbers:

  Ubuntu 22.04.3 LTS
  gnome-shell 42.9-0ubuntu2
  xwayland 2:22.1.1-1ubuntu0.7

  $ ps -aux | grep 'alan .*gnome-shell$'
  alan        9248 26.1  3.4 5492888 269136 ?      Rsl  19:54  30:26 /usr/bin/gnome-shell

  $ sudo strace -p 9248 2>&1|head
  strace: Process 9248 attached
  epoll_wait(37, [{events=EPOLLIN, data={u32=403234816, u64=139797293752320}}], 32, 0) = 1
  recvmsg(21, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\1\0\0\0\0\0\f\0\3\0\0\0", iov_len=752}, {iov_base="", iov_len=3344}], msg_iovlen=2, msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_DONTWAIT|MSG_CMSG_CLOEXEC) = 12
  write(4, "\1\0\0\0\0\0\0\0", 8)         = 8
  sendmsg(21, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\3\0\0\0\0\0\f\0[\2\0\0\1\0\0\0\1\0\f\0\3\0\0\0", iov_len=24}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 24
  poll([{fd=4, events=POLLIN}, {fd=8, events=POLLIN}, {fd=9, events=POLLIN}, {fd=19, events=POLLIN}, {fd=20, events=POLLIN}, {fd=23, events=POLLIN}, {fd=24, events=POLLIN}, {fd=25, events=POLLIN}, {fd=34, events=POLLIN}, {fd=36, events=POLLIN}, {fd=37, events=POLLIN}, {fd=54, events=POLLIN}, {fd=63, events=POLLIN}, {fd=66, events=POLLIN}], 14, 79809702) = 2 ([{fd=4, revents=POLLIN}, {fd=37, revents=POLLIN}])
  read(4, "\2\0\0\0\0\0\0\0", 16)         = 8
  write(4, "\1\0\0\0\0\0\0\0", 8)         = 8
  epoll_wait(37, [{events=EPOLLIN, data={u32=403234816, u64=139797293752320}}], 32, 0) = 1

  The recvmsg() call is here:

  #0  __libc_recvmsg (fd=21, msg=0x7fff1de64a50, flags=1073741888) at ../sysdeps/unix/sysv/linux/recvmsg.c:35
  #1  0x00007f2531ea5ad6 in  () at /lib/x86_64-linux-gnu/libwayland-server.so.0
  #2  0x00007f2531ea4eea in wl_event_loop_dispatch () at /lib/x86_64-linux-gnu/libwayland-server.so.0
  #3  0x00007f2531d2b45b in wayland_event_source_dispatch (base=<optimised out>, callback=<optimised out>, data=<optimised out>)
      at ../src/wayland/meta-wayland.c:110
  #4  0x00007f2532b42d3b in g_main_dispatch (context=0x55c0046cc8f0) at ../../../glib/gmain.c:3419
  #5  g_main_context_dispatch (context=0x55c0046cc8f0) at ../../../glib/gmain.c:4137
  #6  0x00007f2532b98258 in g_main_context_iterate.constprop.0
      (context=0x55c0046cc8f0, block=block at entry=1, dispatch=dispatch at entry=1, self=<optimised out>) at ../../../glib/gmain.c:4213
  #7  0x00007f2532b422b3 in g_main_loop_run (loop=0x55c00698ae30) at ../../../glib/gmain.c:4413
  #8  0x00007f2531cd0b79 in meta_context_run_main_loop (context=context at entry=0x55c0046c70c0, error=error at entry=0x7fff1de64f08)
      at ../src/core/meta-context.c:437
  #9  0x000055c003cf4f12 in main (argc=<optimised out>, argv=<optimised out>) at ../src/main.c:650

  The sendmsg() call is here:

  Thread 1 "gnome-shell" hit Breakpoint 1, __libc_sendmsg (fd=21, msg=0x7fff1de64c50, flags=16448) at ../sysdeps/unix/sysv/linux/sendmsg.c:26
  26	../sysdeps/unix/sysv/linux/sendmsg.c: No such file or directory.
  (gdb) where
  #0  __libc_sendmsg (fd=21, msg=0x7fff1de64c50, flags=16448) at ../sysdeps/unix/sysv/linux/sendmsg.c:26
  #1  0x00007f2531ea1c9d in  () at /lib/x86_64-linux-gnu/libwayland-server.so.0
  #2  0x00007f2531ea565e in wl_display_flush_clients () at /lib/x86_64-linux-gnu/libwayland-server.so.0
  #3  0x00007f2531d2b437 in wayland_event_source_prepare (base=base at entry=0x55c004a374d0, timeout=timeout at entry=0x7fff1de64dc4)
      at ../src/wayland/meta-wayland.c:97
  #4  0x00007f2532b428e7 in g_main_context_prepare (context=0x55c0046cc8f0, priority=0x7fff1de64e50) at ../../../glib/gmain.c:3739
  #5  0x00007f2532b98123 in g_main_context_iterate.constprop.0
      (context=0x55c0046cc8f0, block=block at entry=1, dispatch=dispatch at entry=1, self=<optimised out>) at ../../../glib/gmain.c:4193
  #6  0x00007f2532b422b3 in g_main_loop_run (loop=0x55c00698ae30) at ../../../glib/gmain.c:4413
  #7  0x00007f2531cd0b79 in meta_context_run_main_loop (context=context at entry=0x55c0046c70c0, error=error at entry=0x7fff1de64f08)
      at ../src/core/meta-context.c:437
  #8  0x000055c003cf4f12 in main (argc=<optimised out>, argv=<optimised out>) at ../src/main.c:650

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