From 930267a902d25dbce8ff63b6a1fc190833d63b4b Mon Sep 17 00:00:00 2001
From: Uri Yagelnik <uriy@amazon.com>
Date: Wed, 11 Dec 2024 07:57:24 +0000
Subject: [PATCH] replication: fix io-threads possible race by moving
 waitForClientIO earlier

---
 src/replication.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/replication.c b/src/replication.c
index 8ff8ad3f0f..22a710c291 100644
--- a/src/replication.c
+++ b/src/replication.c
@@ -1036,6 +1036,9 @@ void syncCommand(client *c) {
     /* ignore SYNC if already replica or in monitor mode */
     if (c->flag.replica) return;
 
+    /* Wait for any IO pending operation to finish before changing the client state to replica */
+    waitForClientIO(c);
+
     /* Check if this is a failover request to a replica with the same replid and
      * become a primary if so. */
     if (c->argc > 3 && !strcasecmp(c->argv[0]->ptr, "psync") && !strcasecmp(c->argv[3]->ptr, "failover")) {
@@ -1147,8 +1150,6 @@ void syncCommand(client *c) {
     c->repl_state = REPLICA_STATE_WAIT_BGSAVE_START;
     if (server.repl_disable_tcp_nodelay) connDisableTcpNoDelay(c->conn); /* Non critical if it fails. */
     c->repldbfd = -1;
-    /* Wait for any IO pending operation to finish before changing the client state */
-    waitForClientIO(c);
     c->flag.replica = 1;
     listAddNodeTail(server.replicas, c);