[PATCH] core/pppd-plugin: wait to recover port settings before notifying death

[Alfonso Sánchez-Beato <alfonso sanchez-beato canonical com>]

pppd restores the previous settings for the serial port it uses right
before exiting. It is especially important to do so because otherwise
ModemManager is not able to recover the port as it can receive a hangup
event from the port due to CLOCAL not being restored.  However, there is
currently a race condition that produces this issue. This is because
when PHASE_DEAD is notified, pppd still has not restored the port
settings - it does that a bit later, in the die() function.

This patch delays notifying PHASE_DEAD until when the exitnotify() hook
is called by pppd: when this happens the port settings have already been
restored.

There were previously efforts to fix this in commit fe090c3, so
PHASE_DEAD was used instead of PHASE_DISCONNECT to notify MM that the
port was disconnected, but that still early to ensure that the port
settings are restored.

The MM traces seen when the bug is triggered are:

ModemManager[2158]: <warn>  (ttyACM1): could not re-acquire serial port lock: (5) Input/output error
ModemManager[2158]: <warn>  Couldn't load Operator Code: 'Cannot run sequence: 'Could not open serial device 
ttyACM1: it has been forced close'
---
 src/ppp/nm-pppd-plugin.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/ppp/nm-pppd-plugin.c b/src/ppp/nm-pppd-plugin.c
index 626dcdbd8..f0b9027ca 100644
--- a/src/ppp/nm-pppd-plugin.c
+++ b/src/ppp/nm-pppd-plugin.c
@@ -51,7 +51,7 @@ static struct {
 } gl;
 
 static void
-nm_phasechange (void *data, int arg)
+nm_phasechange (int arg)
 {
        NMPPPStatus ppp_status = NM_PPP_STATUS_UNKNOWN;
        char *ppp_phase;
@@ -167,6 +167,16 @@ nm_phasechange (void *data, int arg)
        }
 }
 
+static void
+nm_phasechange_hook (void *data, int arg)
+{
+       /* We send the nofication in exitnotify instead */
+       if (arg == PHASE_DEAD)
+               return;
+
+       nm_phasechange (arg);
+}
+
 static void
 nm_ip_up (void *data, int arg)
 {
@@ -181,7 +191,7 @@ nm_ip_up (void *data, int arg)
 
        if (!opts.ouraddr) {
                g_warning ("nm-ppp-plugin: didn't receive an internal IP from pppd!");
-               nm_phasechange (NULL, PHASE_DEAD);
+               nm_phasechange (PHASE_DEAD);
                return;
        }
 
@@ -384,6 +394,11 @@ nm_exit_notify (void *data, int arg)
 {
        g_return_if_fail (G_IS_DBUS_CONNECTION (gl.dbus_connection));
 
+       /* We wait until this point to notify dead phase to make sure that
+        * the serial port has recovered already its original settings.
+        */
+       nm_phasechange (PHASE_DEAD);
+
        g_message ("nm-ppp-plugin: cleaning up");
 
        g_clear_object (&gl.dbus_connection);
@@ -435,7 +450,7 @@ plugin_init (void)
        pap_passwd_hook = get_credentials;
        pap_check_hook = get_pap_check;
 
-       add_notifier (&phasechange, nm_phasechange, NULL);
+       add_notifier (&phasechange, nm_phasechange_hook, NULL);
        add_notifier (&ip_up_notifier, nm_ip_up, NULL);
        add_notifier (&exitnotify, nm_exit_notify, NULL);
        add_ip6_notifier ();
-- 
2.17.1