From 972b9776596627a5953792122c1f939556956bc3 Mon Sep 17 00:00:00 2001 From: Ondrej Holy Date: Mon, 10 Feb 2020 16:00:42 +0100 Subject: [PATCH 1/4] gunixmounts: Make GUnixMountMonitor thread-safe The Nautilus test suite often crashes with "GLib-FATAL-CRITICAL: g_source_is_destroyed: assertion 'g_atomic_int_get (&source->ref_count) > 0' failed" if it is started with "GIO_USE_VOLUME_MONITOR=unix". This is because GUnixMountMonitor is simultaneously used from multiple threads over GLocalFile and GVolumeMonitor APIs. Let's add guards for proc_mounts_watch_source and mount_poller_time variables to prevent those crashes. Fixes: https://gitlab.gnome.org/GNOME/glib/issues/2030 --- gio/gunixmounts.c | 36 +++++++++++++++++++++++++++++++----- 1 file changed, 31 insertions(+), 5 deletions(-) diff --git a/gio/gunixmounts.c b/gio/gunixmounts.c index cbf2ee99e..b716f22e4 100644 --- a/gio/gunixmounts.c +++ b/gio/gunixmounts.c @@ -152,7 +152,11 @@ static GList *_g_get_unix_mounts (void); static GList *_g_get_unix_mount_points (void); static gboolean proc_mounts_watch_is_running (void); +G_LOCK_DEFINE_STATIC (proc_mounts_source); + +/* Protected by proc_mounts_source lock */ static guint64 mount_poller_time = 0; +static GSource *proc_mounts_watch_source; #ifdef HAVE_SYS_MNTTAB_H #define MNTOPT_RO "ro" @@ -1485,18 +1489,21 @@ get_mounts_timestamp (void) { const char *monitor_file; struct stat buf; + guint64 timestamp = 0; + + G_LOCK (proc_mounts_source); monitor_file = get_mtab_monitor_file (); /* Don't return mtime for /proc/ files */ if (monitor_file && !g_str_has_prefix (monitor_file, "/proc/")) { if (stat (monitor_file, &buf) == 0) - return (guint64)buf.st_mtime; + timestamp = buf.st_mtime; } else if (proc_mounts_watch_is_running ()) { /* it's being monitored by poll, so return mount_poller_time */ - return mount_poller_time; + timestamp = mount_poller_time; } else { @@ -1505,9 +1512,12 @@ get_mounts_timestamp (void) * return TRUE so any application caches depending on it (like eg. * the one in GIO) get invalidated and don't hold possibly outdated * data - see Bug 787731 */ - return (guint64) g_get_monotonic_time (); + timestamp = g_get_monotonic_time (); } - return 0; + + G_UNLOCK (proc_mounts_source); + + return timestamp; } static guint64 @@ -1704,10 +1714,10 @@ G_DEFINE_TYPE (GUnixMountMonitor, g_unix_mount_monitor, G_TYPE_OBJECT) static GContextSpecificGroup mount_monitor_group; static GFileMonitor *fstab_monitor; static GFileMonitor *mtab_monitor; -static GSource *proc_mounts_watch_source; static GList *mount_poller_mounts; static guint mtab_file_changed_id; +/* Called with proc_mounts_source lock held. */ static gboolean proc_mounts_watch_is_running (void) { @@ -1768,7 +1778,10 @@ proc_mounts_changed (GIOChannel *channel, { if (cond & G_IO_ERR) { + G_LOCK (proc_mounts_source); mount_poller_time = (guint64) g_get_monotonic_time (); + G_UNLOCK (proc_mounts_source); + g_context_specific_group_emit (&mount_monitor_group, signals[MOUNTS_CHANGED]); } @@ -1802,7 +1815,10 @@ mount_change_poller (gpointer user_data) if (has_changed) { + G_LOCK (proc_mounts_source); mount_poller_time = (guint64) g_get_monotonic_time (); + G_UNLOCK (proc_mounts_source); + g_context_specific_group_emit (&mount_monitor_group, signals[MOUNTPOINTS_CHANGED]); } @@ -1819,11 +1835,13 @@ mount_monitor_stop (void) g_object_unref (fstab_monitor); } + G_LOCK (proc_mounts_source); if (proc_mounts_watch_source != NULL) { g_source_destroy (proc_mounts_watch_source); proc_mounts_watch_source = NULL; } + G_UNLOCK (proc_mounts_source); if (mtab_monitor) { @@ -1869,6 +1887,8 @@ mount_monitor_start (void) } else { + G_LOCK (proc_mounts_source); + proc_mounts_watch_source = g_io_create_watch (proc_mounts_channel, G_IO_ERR); g_source_set_callback (proc_mounts_watch_source, (GSourceFunc) proc_mounts_changed, @@ -1877,6 +1897,8 @@ mount_monitor_start (void) g_main_context_get_thread_default ()); g_source_unref (proc_mounts_watch_source); g_io_channel_unref (proc_mounts_channel); + + G_UNLOCK (proc_mounts_source); } } else @@ -1889,6 +1911,8 @@ mount_monitor_start (void) } else { + G_LOCK (proc_mounts_source); + proc_mounts_watch_source = g_timeout_source_new_seconds (3); mount_poller_mounts = _g_get_unix_mounts (); mount_poller_time = (guint64)g_get_monotonic_time (); @@ -1898,6 +1922,8 @@ mount_monitor_start (void) g_source_attach (proc_mounts_watch_source, g_main_context_get_thread_default ()); g_source_unref (proc_mounts_watch_source); + + G_UNLOCK (proc_mounts_source); } } From 898a9c332e5c238bfbac8e64441286dac5ebe61e Mon Sep 17 00:00:00 2001 From: Ondrej Holy Date: Tue, 18 Feb 2020 09:10:03 +0100 Subject: [PATCH 2/4] gunixmounts: Prevent invalid time_read timestamps The `get_mounts_timestamp()` function uses `mount_poller_time` when `proc_mounts_watch_source` is set, but the `mount_poller_time` is not initialized in the same time as `proc_mounts_watch_source`. This may cause that zero, or some outdated value is returned. Let's initialize `mount_poller_time` to prevent invalid values to be returned. --- gio/gunixmounts.c | 1 + 1 file changed, 1 insertion(+) diff --git a/gio/gunixmounts.c b/gio/gunixmounts.c index b716f22e4..8b12d8fbc 100644 --- a/gio/gunixmounts.c +++ b/gio/gunixmounts.c @@ -1890,6 +1890,7 @@ mount_monitor_start (void) G_LOCK (proc_mounts_source); proc_mounts_watch_source = g_io_create_watch (proc_mounts_channel, G_IO_ERR); + mount_poller_time = (guint64) g_get_monotonic_time (); g_source_set_callback (proc_mounts_watch_source, (GSourceFunc) proc_mounts_changed, NULL, NULL); From ab278c0072f8e690ca4e7c3143a979dcc06e0a44 Mon Sep 17 00:00:00 2001 From: Ondrej Holy Date: Mon, 17 Feb 2020 11:05:07 +0100 Subject: [PATCH 3/4] gunixmounts: Prevent race when mtab file changed mtab_file_changed_id might be set on thread default context, but it is always cleared on the global context because of usage of g_idle_add. This can cause the emission of redundant "mounts-change" signals. This should not cause any issues to the client application, but let's attach the idle source to the thread-default context instead to avoid those races for sure. --- gio/gunixmounts.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/gio/gunixmounts.c b/gio/gunixmounts.c index 8b12d8fbc..1f7077c11 100644 --- a/gio/gunixmounts.c +++ b/gio/gunixmounts.c @@ -1756,6 +1756,9 @@ mtab_file_changed (GFileMonitor *monitor, GFileMonitorEvent event_type, gpointer user_data) { + GMainContext *context; + GSource *source; + if (event_type != G_FILE_MONITOR_EVENT_CHANGED && event_type != G_FILE_MONITOR_EVENT_CREATED && event_type != G_FILE_MONITOR_EVENT_DELETED) @@ -1768,7 +1771,16 @@ mtab_file_changed (GFileMonitor *monitor, if (mtab_file_changed_id > 0) return; - mtab_file_changed_id = g_idle_add (mtab_file_changed_cb, NULL); + context = g_main_context_get_thread_default (); + if (!context) + context = g_main_context_default (); + + source = g_idle_source_new (); + g_source_set_priority (source, G_PRIORITY_DEFAULT); + g_source_set_callback (source, mtab_file_changed_cb, NULL, NULL); + g_source_set_name (source, "[gio] mtab_file_changed_cb"); + g_source_attach (source, context); + g_source_unref (source); } static gboolean From 501558eaa12d2b7fb61815a96d56b97ea1b5656b Mon Sep 17 00:00:00 2001 From: Ondrej Holy Date: Mon, 17 Feb 2020 11:20:17 +0100 Subject: [PATCH 4/4] gunixmounts: Remove pending sources when finalizing mtab_file_changed_id is not currently removed when finalizing, which could potentially lead to segfaults. Let's remove the source when finalizing to avoid this. --- gio/gunixmounts.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/gio/gunixmounts.c b/gio/gunixmounts.c index 1f7077c11..1880d9926 100644 --- a/gio/gunixmounts.c +++ b/gio/gunixmounts.c @@ -1861,6 +1861,12 @@ mount_monitor_stop (void) g_object_unref (mtab_monitor); } + if (mtab_file_changed_id) + { + g_source_remove (mtab_file_changed_id); + mtab_file_changed_id = 0; + } + g_list_free_full (mount_poller_mounts, (GDestroyNotify) g_unix_mount_free); }