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Merge branch 'benzea/fix-inotify-race' into 'main'

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glocalfilemonitor: Avoid file monitor destruction from event thread

Closes #1941

See merge request GNOME/glib!2561
This commit is contained in:
Philip Withnall 2022-05-31 12:18:38 +00:00
commit c1f8865689
2 changed files with 72 additions and 7 deletions
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27
gio/glocalfilemonitor.c
View File

@ -350,7 +350,6 @@ g_file_monitor_source_handle_event (GFileMonitorSource *fms,
gint64 event_time)
{
gboolean interesting = TRUE;
GFileMonitor *instance = NULL;
g_assert (!child || is_basename (child));
g_assert (!rename_to || is_basename (rename_to));
@ -361,9 +360,24 @@ g_file_monitor_source_handle_event (GFileMonitorSource *fms,
g_mutex_lock (&fms->lock);
/* monitor is already gone -- don't bother */
instance = g_weak_ref_get (&fms->instance_ref);
if (instance == NULL)
/* NOTE:
*
* We process events even if the file monitor has already been disposed.
* The reason is that we must not take a reference to the instance here as
* destroying it from the event handling thread will lead to a deadlock when
* taking the lock in _ih_sub_cancel.
*
* This results in seemingly-unbounded growth of the `event_queue` with the
* calls to `g_file_monitor_source_queue_event()`. However, each of those sets
* the ready time on the #GSource, which means that it will be dispatched in
* a subsequent iteration of the #GMainContext it’s attached to. At that
* point, `g_file_monitor_source_dispatch()` will return %FALSE, and this will
* trigger finalisation of the source. That will clear the `event_queue`.
*
* If the source is no longer attached, this will return early to prevent
* unbounded queueing.
*/
if (g_source_is_destroyed ((GSource *) fms))
{
g_mutex_unlock (&fms->lock);
return TRUE;
@ -454,7 +468,6 @@ g_file_monitor_source_handle_event (GFileMonitorSource *fms,
g_file_monitor_source_update_ready_time (fms);
g_mutex_unlock (&fms->lock);
g_clear_object (&instance);
return interesting;
}
@ -601,9 +614,9 @@ g_file_monitor_source_dispose (GFileMonitorSource *fms)
g_file_monitor_source_update_ready_time (fms);
g_mutex_unlock (&fms->lock);
g_source_destroy ((GSource *) fms);
g_mutex_unlock (&fms->lock);
}
static void

52
gio/tests/testfilemonitor.c
View File

@ -1036,6 +1036,57 @@ test_file_hard_links (Fixture *fixture,
g_object_unref (data.output_stream);
}
static void
test_finalize_in_callback (Fixture *fixture,
gconstpointer user_data)
{
GFile *file = NULL;
guint i;
g_test_summary ("Test that finalization of a GFileMonitor in one of its "
"callbacks doesn’t cause a deadlock.");
g_test_bug ("https://gitlab.gnome.org/GNOME/glib/-/issues/1941");
file = g_file_get_child (fixture->tmp_dir, "race-file");
for (i = 0; i < 50; i++)
{
GFileMonitor *monitor = NULL;
GError *local_error = NULL;
/* Monitor the file. */
monitor = g_file_monitor_file (file, G_FILE_MONITOR_NONE, NULL, &local_error);
g_assert_no_error (local_error);
g_assert_nonnull (monitor);
/* Create the file. */
g_file_replace_contents (file, "hello", 5, NULL, FALSE,
G_FILE_CREATE_NONE, NULL, NULL, &local_error);
g_assert_no_error (local_error);
/* Immediately drop the last ref to the monitor in the hope that this
* happens in the middle of the critical section in
* g_file_monitor_source_handle_event(), so that any cleanup at the end
* of that function is done with a now-finalised file monitor. */
g_object_unref (monitor);
/* Re-create the monitor and do the same again for deleting the file, to
* give a second chance at hitting the race condition. */
monitor = g_file_monitor_file (file, G_FILE_MONITOR_NONE, NULL, &local_error);
g_assert_no_error (local_error);
g_assert_nonnull (monitor);
/* Delete the file. */
g_file_delete (file, NULL, &local_error);
g_assert_no_error (local_error);
/* Drop the ref again. */
g_object_unref (monitor);
}
g_object_unref (file);
}
int
main (int argc, char *argv[])
{
@ -1047,6 +1098,7 @@ main (int argc, char *argv[])
g_test_add ("/monitor/dir-not-existent", Fixture, NULL, setup, test_dir_non_existent, teardown);
g_test_add ("/monitor/cross-dir-moves", Fixture, NULL, setup, test_cross_dir_moves, teardown);
g_test_add ("/monitor/file/hard-links", Fixture, NULL, setup, test_file_hard_links, teardown);
g_test_add ("/monitor/finalize-in-callback", Fixture, NULL, setup, test_finalize_in_callback, teardown);
return g_test_run ();
}