From: Vsevolod Stakhov <vsevolod@rspamd.com>
Date: Sat, 21 Mar 2026 13:36:18 +0000 (+0000)
Subject: [Fix] Fix CPU busy-loop in fuzzy TCP client due to EV_WRITE not being cleared
X-Git-Tag: 4.0.0~20
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=06dba4495b170ea4733609dabf60a52b122d4e77;p=thirdparty%2Frspamd.git

[Fix] Fix CPU busy-loop in fuzzy TCP client due to EV_WRITE not being cleared

When the TCP write queue drained, EV_WRITE was left armed on the socket
watcher. Since a connected TCP socket is always writable, libev fired
EV_WRITE continuously causing 100% CPU usage. The UDP path correctly
switched to EV_READ only after writing.

- Drop EV_WRITE when write queue empties in fuzzy_tcp_write_handler
- Only arm EV_WRITE on connection established if data is actually queued
- Remove redundant per-IO fuzzy_tcp_check_pending_timeouts call (timer
  callback already handles this), which amplified the spin with O(N)
  hash scans and GHashTable allocations on every iteration
---

diff --git a/src/plugins/fuzzy_check.c b/src/plugins/fuzzy_check.c
index 73ebf9cf2f..f1788cfd2c 100644
--- a/src/plugins/fuzzy_check.c
+++ b/src/plugins/fuzzy_check.c
@@ -1161,9 +1161,9 @@ fuzzy_tcp_io_handler(int fd, short what, gpointer ud)
 
 			rspamd_upstream_ok(conn->server);
 
-			/* Now wait for both read and write events */
+			/* Start reading; only arm EV_WRITE if there's queued data */
 			rspamd_ev_watcher_reschedule(conn->event_loop, &conn->ev,
-										 EV_READ | EV_WRITE);
+										 g_queue_is_empty(conn->write_queue) ? EV_READ : EV_READ | EV_WRITE);
 
 			msg_debug("fuzzy_tcp: after reschedule - fd=%d, ev.io.fd=%d",
 					  conn->fd, (int) conn->ev.io.fd);
@@ -1179,11 +1179,6 @@ fuzzy_tcp_io_handler(int fd, short what, gpointer ud)
 		fuzzy_tcp_read_handler(conn);
 	}
 
-	/* Check for timed out pending requests */
-	if (conn->connected) {
-		fuzzy_tcp_check_pending_timeouts(conn->rule, conn->last_activity);
-	}
-
 	FUZZY_TCP_RELEASE(conn);
 }
 
@@ -1267,8 +1262,8 @@ fuzzy_tcp_write_handler(struct fuzzy_tcp_connection *conn)
 		}
 	}
 
-	/* Queue is empty, no more data to write */
-	/* Might want to disable EV_WRITE here if needed */
+	/* Queue is empty, switch to read-only to avoid busy-looping on EV_WRITE */
+	rspamd_ev_watcher_reschedule(conn->event_loop, &conn->ev, EV_READ);
 }
 
 /**