BUG/MEDIUM: stream-int: don't subscribed for recv when we're trying to flush data

If we cannot splice incoming data using rcv_pipe() due to remaining data
in the buffer, we must not subscribe to the mux but instead tag the
stream-int as blocked on missing Rx room. Otherwise when data are
flushed, calling si_chk_rcv() will have no effect because the WAIT_EP
flag remains present, and we'll end in an rx timeout. This case is very
hard to reproduce, and requires an inversion of the polling side in the
middle of a transfer. This can only happen when the client and the server
are using similar links and when splicing is enabled. It typically takes
hundreds of MB to GB for the problem to happen, and tends to be magnified
by the use of option contstats which causes process_stream() to be called
every 5s and to try again to recv.

This fix must be backported to 2.1, 2.0, and possibly 1.9.

diff --git a/src/stream_interface.c b/src/stream_interface.c
index e673e0f5a535be66c8e8d455911cde927078e70a..aa9cf203247f9cf35d6e5445fddaf84d90813a11 100644 (file)
--- a/src/stream_interface.c
+++ b/src/stream_interface.c
@@ -1355,6 +1355,13 @@ int si_cs_recv(struct conn_stream *cs)
                }
 
                if (ret <= 0) {
+                       /* if we refrained from reading because we asked for a
+                        * flush to satisfy rcv_pipe(), we must not subscribe
+                        * and instead report that there's not enough room
+                        * here to proceed.
+                        */
+                       if (flags & CO_RFL_BUF_FLUSH)
+                               si_rx_room_blk(si);
                        break;
                }