proxy: Add a 30-second timeout for requests in-flight to upstream

It's a little more complicated than that, actually. For the various
states that involve reading from, or writing to, the upstream fd,
if the amount of time spent in that state is > 30 seconds, we reconnect
to the server and resend the request.

we also introduce a 15-second reconnect dampener to keep us from stressing
things unduly. This may need to be decreased, or turned into an exponential
backoff, at some point.

src/proxy.c

@@ -266,6 +266,12 @@ static char* proxy_session_state_names[] = {
   "READ_FROM_UPSTREAM"
 };
 
+static inline int proxy_state_upstream( int state )
+{
+	return state == CONNECT_TO_UPSTREAM || state == READ_INIT_FROM_UPSTREAM ||
+	       state == WRITE_TO_UPSTREAM   || state == READ_FROM_UPSTREAM;
+}
+
 #ifdef PREFETCH
 
 int proxy_prefetch_for_request( struct proxier* proxy, int state )
@@ -343,7 +349,6 @@ int proxy_prefetch_for_request( struct proxier* proxy, int state )
 
 		debug( "Prefetching %"PRIu32" bytes", req->len - proxy->prefetch_req_orig_len );
 		nbd_h2r_request( req, req_raw );
-		debug( "Request len: %"PRIu32" ; raw: %"PRIu32, req->len, req_raw->len );
 	}
 
 	return state;
@@ -629,11 +634,18 @@ int proxy_write_to_downstream( struct proxier* proxy, int state )
  */
 void proxy_session( struct proxier* proxy )
 {
+	uint64_t state_started;
+	int old_state = EXIT;
+	int state;
+	int connect_to_upstream_cooldown = 0;
+
+
 	/* First action: Write hello to downstream */
 	nbd_hello_to_buf( (struct nbd_init_raw *) proxy->rsp.buf, proxy->upstream_size );
 	proxy->rsp.size = sizeof( struct nbd_init_raw );
 	proxy->rsp.needle = 0;
-	int state = WRITE_TO_DOWNSTREAM;
+	state = WRITE_TO_DOWNSTREAM;
+
 
 	info( "Beginning proxy session on fd %i", proxy->downstream_fd );
 
@@ -654,7 +666,19 @@ void proxy_session( struct proxier* proxy )
 		FD_ZERO( &rfds );
 		FD_ZERO( &wfds );
 
-		debug( "Proxy is in state %s ( %i )", proxy_session_state_names[state], state );
+		if ( state != old_state ) {
+			state_started = monotonic_time_ms();
+
+			debug(
+				"State transitition from %s to %s",
+				proxy_session_state_names[old_state],
+				proxy_session_state_names[state]
+			);
+		} else {
+			debug( "Proxy is in state %s", proxy_session_state_names[state], state );
+		}
+
+		old_state = state;
 
 		switch( state ) {
 			case READ_FROM_DOWNSTREAM:
@@ -668,18 +692,23 @@ void proxy_session( struct proxier* proxy )
 				FD_SET(proxy->upstream_fd, &wfds );
 				break;
 			case CONNECT_TO_UPSTREAM:
+				/* upstream_fd is now -1 */
 				proxy_disconnect_from_upstream( proxy );
-				/* Changes proxy->upstream_fd */
-				proxy_start_connect_to_upstream( proxy );
 
-				if ( proxy->upstream_fd == -1 ) {
-					warn( SHOW_ERRNO( "Error acquiring socket to upstream" ) );
-					continue;
+				if ( connect_to_upstream_cooldown ) {
+					connect_to_upstream_cooldown = 0;
+				} else {
+					proxy_start_connect_to_upstream( proxy );
+
+					if ( proxy->upstream_fd == -1 ) {
+						warn( SHOW_ERRNO( "Error acquiring socket to upstream" ) );
+						continue;
+					}
+					FD_SET( proxy->upstream_fd, &wfds );
 				}
-
-				/* non-blocking connect() */
+				/* non-blocking connect() or a simple sleep */
 				select_timeout.tv_sec = 15;
-				FD_SET( proxy->upstream_fd, &wfds );
+
 				break;
 			case READ_INIT_FROM_UPSTREAM:
 			case READ_FROM_UPSTREAM:
@@ -699,6 +728,11 @@ void proxy_session( struct proxier* proxy )
 			break;
 		}
 
+		/* Happens after failed reconnect. Avoid SIGBUS on FD_ISSET() */
+		if ( proxy->upstream_fd == -1 ) {
+			continue;
+		}
+
 		switch( state ) {
 			case READ_FROM_DOWNSTREAM:
 				if ( FD_ISSET( proxy->downstream_fd, &rfds ) ) {
@@ -717,7 +751,12 @@ void proxy_session( struct proxier* proxy )
 				if ( FD_ISSET( proxy->upstream_fd, &wfds ) ) {
 					state = proxy_continue_connecting_to_upstream( proxy, state );
 				}
-				/* Leaving state untouched will retry connecting to upstream */
+				/* Leaving state untouched will retry connecting to upstream -
+				 * so introduce a bit of sleep  */
+				if ( state == CONNECT_TO_UPSTREAM )  {
+					connect_to_upstream_cooldown = 1;
+				}
+
 				break;
 			case READ_INIT_FROM_UPSTREAM:
 				state = proxy_read_init_from_upstream( proxy, state );
@@ -744,6 +783,17 @@ void proxy_session( struct proxier* proxy )
 				break;
 		}
 
+		/* In these states, we're interested in restarting after a timeout.
+		 */
+		if ( old_state == state && proxy_state_upstream( state ) ) {
+			if ( ( monotonic_time_ms() ) - state_started > UPSTREAM_TIMEOUT ) {
+				warn(
+					"Timed out in state %s while communicating with upstream",
+					proxy_session_state_names[state]
+				);
+				state = CONNECT_TO_UPSTREAM;
+			}
+		}
 	}
 
 	info(

src/proxy.h

@@ -14,6 +14,12 @@
   #include "prefetch.h"
 #endif
 
+/** UPSTREAM_TIMEOUT
+ * How long ( in ms ) to allow for upstream to respond. If it takes longer
+ * than this, we will cancel the current request-response to them and resubmit
+ */
+#define UPSTREAM_TIMEOUT 30 * 1000
+
 struct proxier {
 	/* The flexnbd wrapper this proxier is attached to */
 	struct flexnbd*   flexnbd;