varlink: disconnect varlink link in one more case

Previously we'd possibly see POLLHUP on a varlink link, and continue to
run epoll on it even though we have nothing to read nor write anymore.

Let's fix that, and once we know that there's nothing to write anymore
(or we saw a write error already) we'll disconnect after POLLHUP.

Fixes: #20062
(cherry picked from commit 7c26a631ad8bf91016db156b7d299ca68fd7866e)

diff --git a/src/shared/varlink.c b/src/shared/varlink.c
index 8da568e2080f36f86042cb4d0e0bd1a31192d8b7..a57475b5ba967b33a53c1d7fe2dc13ae5aa0b47b 100644 (file)
--- a/src/shared/varlink.c
+++ b/src/shared/varlink.c
@@ -417,9 +417,10 @@ static int varlink_test_disconnect(Varlink *v) {
         if (IN_SET(v->state, VARLINK_IDLE_CLIENT) && (v->write_disconnected || v->got_pollhup))
                 goto disconnect;
 
-        /* The server is still expecting to write more, but its write end is disconnected and it got a POLLHUP
-         * (i.e. from a disconnected client), so disconnect. */
-        if (IN_SET(v->state, VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE) && v->write_disconnected && v->got_pollhup)
+        /* We are on the server side and still want to send out more replies, but we saw POLLHUP already, and
+         * either got no buffered bytes to write anymore or already saw a write error. In that case we should
+         * shut down the varlink link. */
+        if (IN_SET(v->state, VARLINK_PENDING_METHOD, VARLINK_PENDING_METHOD_MORE) && (v->write_disconnected || v->output_buffer_size == 0) && v->got_pollhup)
                 goto disconnect;
 
         return 0;