Re: [PATCH 1/5] lib: Don't unref message passed to virGDBusCallMethod{WithFD}()

On 10/2/20 11:52 AM, Pavel Hrdina wrote: > On Fri, Oct 02, 2020 at 11:22:06AM +0200, Michal Privoznik wrote: > > The virGDBusCallMethod() and virGDBusCallMethodWithFD() are > > simple wrappers over g_dbus_connection_call_sync() and > > g_dbus_connection_call_with_unix_fd_list_sync() respectively. The > > documentation to these function states that passed parameters > > (@message in our case) is consumed for 'convenient' inline use of > > g_variant_new() [1]. But that means we must not unref the message > > afterwards. To make it explicit that the message is consumed the > > signature of our wrappers is changed too. > > > > 1: https://developer.gnome.org/gio/stable/GDBusConnection.html#g-dbus-connec... > > > > Reported-by: Cole Robinson <crobinso(a)redhat.com&gt; > > Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; > > --- > > src/rpc/virnetdaemon.c | 4 ++-- > > src/util/virfirewalld.c | 16 ++++++++-------- > > src/util/virgdbus.c | 29 ++++++++++++++++++++--------- > > src/util/virgdbus.h | 4 ++-- > > src/util/virpolkit.c | 4 ++-- > > src/util/virsystemd.c | 23 ++++++++--------------- > > 6 files changed, 42 insertions(+), 38 deletions(-) > > This doesn't look right, I know about the limitation and was counting > with it when introducing virgdbus.c where we call g_variant_ref_sink() > on the passed message. > > g_variant_new() returns floating reference which makes it possible to us > it as described in the g_dbus_connection_call_sync() documentation but > for our convenience I changed the behavior in virGDBusCallMethod() to > make it a normal reference so it is not consumed. The motivation was to > not introduce a new reference concept into libvirt code. > > I'll look into the issue but this should not happen. If you look into > g_dbus_connection_call_sync() code in GLib they call > g_variant_ref_sink() on the passed data as well and if they receive a > normal reference they will simply add a new normal reference instead of > consuming it. > > In addition the GLib g_dbus_connection_call_sync() should not be called > from our tests because we mock this call. > > I'll look again into the issue to figure out what's wrong. g_variant_ref_sink() does not do what you think. Here's the code: GVariant * g_variant_ref_sink (GVariant *value) { g_return_val_if_fail (value != NULL, NULL); g_return_val_if_fail (!g_atomic_ref_count_compare (&value->ref_count, 0), NULL); g_variant_lock (value); if (~value->state & STATE_FLOATING) g_variant_ref (value); else value->state &= ~STATE_FLOATING; g_variant_unlock (value); return value; } So if the variant has STATE_FLOATING bit set (which it does), it doesn't increase the refcounter. It just clears it.