[Bug 1890313] Re: GFileMonitor deadlocks

Thu May 6 08:58:52 UTC 2021

This bug was fixed in the package libxmlb - 0.1.15-2ubuntu1~20.04.1

---------------
libxmlb (0.1.15-2ubuntu1~20.04.1) focal; urgency=medium

  * No-change backport from hirsute to focal

libxmlb (0.1.15-2ubuntu1) hirsute; urgency=medium

  * d/p/xb-silo-Cancel-the-GFileMonitor-before-unreffing-it.patch:
    Cherry-pick upstream patch to fix a deadlock. Forwarded to Debian at
    https://salsa.debian.org/efi-team/libxmlb/-/merge_requests (LP: #1890313)

 -- Iain Lane <iain at orangesquash.org.uk>  Mon, 25 Jan 2021 16:05:07
+0000

** Changed in: libxmlb (Ubuntu Focal)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1890313

Title:
  GFileMonitor deadlocks

Status in libxmlb package in Ubuntu:
  Fix Released
Status in libxmlb source package in Focal:
  Fix Released
Status in libxmlb source package in Groovy:
  Fix Released

Bug description:
  [ Description ]

  https://autopkgtest.ubuntu.com/packages/libx/libxmlb/groovy/amd64

  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac
  /autopkgtest-
  groovy/groovy/amd64/libx/libxmlb/20200803_212158_ebe4f@/log.gz :

  ...
  (/usr/libexec/installed-tests/libxmlb/xb-self-test:1066): XbSilo-DEBUG: 21:16:46.741: /tmp/temp.xml changed, invalidating
  Executing: libxmlb/libxmlb.test
  Executing: libxmlb/libxmlb.test
  ...
  Executing: libxmlb/libxmlb.test
  Executing: libxmlb/libxmlb.test
  Executing: libxmlb/libxmlb.test
  Executing: libxmlb/libxmlb.test
  Test timed out after 300 seconds
  Executing: libxmlb/libxmlb.test
  FAIL: libxmlb/libxmlb.test (Child process killed by signal 9)
  SUMMARY: total=1; passed=0; skipped=0; failed=1; user=0.0s; system=0.0s; maxrss=5900
  FAIL: libxmlb/libxmlb.test (Child process killed by signal 9)
  ...

  The backtrace while the test is hanging looks like:

  (gdb) bt
  #0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  #1  0x00007fc9150d57cc in g_mutex_lock_slowpath (mutex=mutex at entry=0x7fc9153a0318 <g.inotify_lock_lock>)
      at ../../../glib/gthread-posix.c:1458
  #2  0x00007fc9150d6256 in g_mutex_lock (mutex=mutex at entry=0x7fc9153a0318 <g.inotify_lock_lock>) at ../../../glib/gthread-posix.c:1482
  #3  0x00007fc915309de4 in _ih_sub_cancel (sub=0x55a566f5be10) at ../../../gio/inotify/inotify-helper.c:121
  #4  0x00007fc91530a06e in g_inotify_file_monitor_cancel (monitor=0x55a566f501a0) at ../../../gio/inotify/ginotifyfilemonitor.c:75
  #5  0x00007fc91523680b in g_file_monitor_cancel (monitor=0x55a566f501a0) at ../../../gio/gfilemonitor.c:241
  #6  g_file_monitor_cancel (monitor=0x55a566f501a0) at ../../../gio/gfilemonitor.c:235
  #7  0x00007fc915236890 in g_file_monitor_dispose (object=0x55a566f501a0) at ../../../gio/gfilemonitor.c:123
  #8  0x00007fc9152fe8b3 in g_local_file_monitor_dispose (object=0x55a566f501a0) at ../../../gio/glocalfilemonitor.c:814
  #9  0x00007fc915179c93 in g_object_unref (_object=<optimized out>) at ../../../gobject/gobject.c:3461
  #10 g_object_unref (_object=0x55a566f501a0) at ../../../gobject/gobject.c:3391
  #11 0x000055a5666dce9d in xb_silo_file_monitor_item_free (item=0x55a566f53810) at ../src/xb-silo.c:1220
  #12 0x00007fc915075172 in g_hash_table_remove_all_nodes (hash_table=hash_table at entry=0x55a566f62b60, notify=notify at entry=1, 
      destruction=destruction at entry=1) at ../../../glib/ghash.c:706
  #13 0x00007fc915076533 in g_hash_table_remove_all_nodes (destruction=1, notify=1, hash_table=0x55a566f62b60)
      at ../../../glib/ghash.c:1461
  #14 g_hash_table_unref (hash_table=0x55a566f62b60) at ../../../glib/ghash.c:1461
  #15 0x000055a5666dd445 in xb_silo_finalize (obj=0x55a566f47a00) at ../src/xb-silo.c:1320
  #16 0x00007fc915179d0e in g_object_unref (_object=<optimized out>) at ../../../gobject/gobject.c:3499
  #17 g_object_unref (_object=0x55a566f47a00) at ../../../gobject/gobject.c:3391
  #18 0x000055a5666c4864 in xb_builder_finalize (obj=0x55a566f46da0) at ../src/xb-builder.c:1027
  #19 0x00007fc915179d0e in g_object_unref (_object=<optimized out>) at ../../../gobject/gobject.c:3499
  #20 g_object_unref (_object=0x55a566f46da0) at ../../../gobject/gobject.c:3391
  #21 0x000055a5666db999 in glib_autoptr_clear_GObject (_ptr=0x55a566f46da0) at /usr/include/glib-2.0/gobject/gobject-autocleanups.h:27
  #22 glib_autoptr_clear_XbBuilder (_ptr=0x55a566f46da0) at ../src/xb-builder.h:20
  #23 glib_autoptr_cleanup_XbBuilder (_ptr=<synthetic pointer>) at ../src/xb-builder.h:20
  #24 xb_builder_ensure_watch_source_func () at ../src/xb-self-test.c:501
  #25 0x00007fc9150b13ce in test_case_run (tc=0x55a566f43b00) at ../../../glib/gtestutils.c:2633
  #26 g_test_run_suite_internal (suite=suite at entry=0x55a566f42440, path=path at entry=0x0) at ../../../glib/gtestutils.c:2721
  #27 0x00007fc9150b1174 in g_test_run_suite_internal (suite=suite at entry=0x55a566f42420, path=path at entry=0x0)
      at ../../../glib/gtestutils.c:2733
  #28 0x00007fc9150b18ba in g_test_run_suite (suite=0x55a566f42420) at ../../../glib/gtestutils.c:2808
  #29 0x00007fc9150b18d5 in g_test_run () at ../../../glib/gtestutils.c:2043
  #30 0x000055a5666c38bb in main (argc=<optimized out>, argv=<optimized out>) at ../src/xb-self-test.c:2423
  (gdb) 

  [ Fix ]

  This is a hang when disposing the GFileMonitor.

  See https://gitlab.gnome.org/GNOME/glib/-/issues/1941 for more
  details.

  The fix is to explicitly cancel the GFileMonitor when when unreffing
  it.

  [ QA ]

  We don't have a testcase for the bug in real usage. It's quite easy to
  check in autopkgtest though. Check the autopkgtests stop being
  flaky/racy with the new version.

  [ What could go wrong ]

  We're cancelling the file monitor explicitly now. Previously this was
  happening internally. This is a pattern used by other glib-using
  projects, but if it's bad then it may be that something goes wrong
  with the file monitor.

  [ Other information ]

  I'll stage this following
  https://wiki.ubuntu.com/StableReleaseUpdates#Staging_an_upload.

  Although this is a bug that could arguably affect users too (the fix
  is not limited to test code). So it may fix a real hang bug which we
  just didn't notice - or get reported - yet. I think it *could* be
  released to users.

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