chardev: fix incorrect unref of source

glib reported error when pty chardev used:

$ ./qemu-system-x86_64 -chardev pty,id=foo -device isa-serial,chardev=foo
qemu-system-x86_64: -chardev pty,id=foo: char device redirected to /dev/pts/2 (label foo)
(qemu-system-x86_64:27885): GLib-CRITICAL **: g_source_unref: assertion 'source != NULL' failed
(qemu-system-x86_64:27885): GLib-CRITICAL **: g_source_unref: assertion 'source != NULL' failed

This patch fixes that.

Fixes: 2c716ba1 ("chardev: introduce qemu_chr_timeout_add_ms()")
CC: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <20180118052049.31119-1-peterx@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

chardev/char-pty.c

@@ -51,15 +51,32 @@ typedef struct {
 static void pty_chr_update_read_handler_locked(Chardev *chr);
 static void pty_chr_state(Chardev *chr, int connected);
 
+static void pty_chr_timer_cancel(PtyChardev *s)
+{
+    if (s->timer_src) {
+        g_source_destroy(s->timer_src);
+        g_source_unref(s->timer_src);
+        s->timer_src = NULL;
+    }
+}
+
+static void pty_chr_open_src_cancel(PtyChardev *s)
+{
+    if (s->open_source) {
+        g_source_destroy(s->open_source);
+        g_source_unref(s->open_source);
+        s->open_source = NULL;
+    }
+}
+
 static gboolean pty_chr_timer(gpointer opaque)
 {
     struct Chardev *chr = CHARDEV(opaque);
     PtyChardev *s = PTY_CHARDEV(opaque);
 
     qemu_mutex_lock(&chr->chr_write_lock);
-    s->timer_src = NULL;
-    g_source_unref(s->open_source);
-    s->open_source = NULL;
+    pty_chr_timer_cancel(s);
+    pty_chr_open_src_cancel(s);
     if (!s->connected) {
         /* Next poll ... */
         pty_chr_update_read_handler_locked(chr);
@@ -68,15 +85,6 @@ static gboolean pty_chr_timer(gpointer opaque)
     return FALSE;
 }
 
-static void pty_chr_timer_cancel(PtyChardev *s)
-{
-    if (s->timer_src) {
-        g_source_destroy(s->timer_src);
-        g_source_unref(s->timer_src);
-        s->timer_src = NULL;
-    }
-}
-
 /* Called with chr_write_lock held.  */
 static void pty_chr_rearm_timer(Chardev *chr, int ms)
 {
@@ -195,11 +203,7 @@ static void pty_chr_state(Chardev *chr, int connected)
     PtyChardev *s = PTY_CHARDEV(chr);
 
     if (!connected) {
-        if (s->open_source) {
-            g_source_destroy(s->open_source);
-            g_source_unref(s->open_source);
-            s->open_source = NULL;
-        }
+        pty_chr_open_src_cancel(s);
         remove_fd_in_watch(chr);
         s->connected = 0;
         /* (re-)connect poll interval for idle guests: once per second.