Retry when a blocked connection system call is interrupted by a signal (#9629)

When repl-diskless-load is enabled, the connection is set to the blocking state.
The connection may be interrupted by a signal during a system call.
This would have resulted in a disconnection and possibly a reconnection loop.

Co-authored-by: Oran Agra <oran@redislabs.com>

src/connection.h

@@ -31,6 +31,8 @@
 #ifndef __REDIS_CONNECTION_H
 #define __REDIS_CONNECTION_H
 
+#include <sys/errno.h>
+
 #define CONN_INFO_LEN   32
 
 struct aeEventLoop;
@@ -149,7 +151,11 @@ static inline int connWrite(connection *conn, const void *data, size_t data_len)
  * connGetState() to see if the connection state is still CONN_STATE_CONNECTED.
  */
 static inline int connRead(connection *conn, void *buf, size_t buf_len) {
-    return conn->type->read(conn, buf, buf_len);
+    int ret = conn->type->read(conn, buf, buf_len);
+    if (ret == -1 && conn->last_errno == EINTR) {
+        conn->state = CONN_STATE_CONNECTED;
+    }
+    return ret;
 }
 
 /* Register a write handler, to be called when the connection is writable.
@@ -203,6 +209,10 @@ static inline int connGetType(connection *conn) {
     return conn->type->get_type(conn);
 }
 
+static inline int connLastErrorRetryable(connection *conn) {
+    return conn->last_errno == EINTR;
+}
+
 connection *connCreateSocket();
 connection *connCreateAcceptedSocket(int fd);
 

src/rio.c

@@ -245,6 +245,7 @@ static size_t rioConnRead(rio *r, void *buf, size_t len) {
                           (char*)r->io.conn.buf + sdslen(r->io.conn.buf),
                           toread);
         if (retval <= 0) {
+            if (connLastErrorRetryable(r->io.conn.conn)) continue;
             if (errno == EWOULDBLOCK) errno = ETIMEDOUT;
             return 0;
         }
@@ -352,6 +353,7 @@ static size_t rioFdWrite(rio *r, const void *buf, size_t len) {
     while(nwritten != len) {
         retval = write(r->io.fd.fd,p+nwritten,len-nwritten);
         if (retval <= 0) {
+            if (retval == -1 && errno == EINTR) continue;
             /* With blocking io, which is the sole user of this
              * rio target, EWOULDBLOCK is returned only because of
              * the SO_SNDTIMEO socket option, so we translate the error

tests/integration/replication.tcl

@@ -996,3 +996,41 @@ start_server {tags {"repl external:skip"}} {
         }
     }
 }
+
+test {replica can handle EINTR if use diskless load} {
+    start_server {tags {"repl"}} {
+        set replica [srv 0 client]
+        set replica_log [srv 0 stdout]
+        start_server {} {
+            set master [srv 0 client]
+            set master_host [srv 0 host]
+            set master_port [srv 0 port]
+
+            $master debug populate 100 master 100000
+            $master config set rdbcompression no
+            $master config set repl-diskless-sync yes
+            $master config set repl-diskless-sync-delay 0
+            $replica config set repl-diskless-load on-empty-db
+            # Construct EINTR error by using the built in watchdog
+            $replica config set watchdog-period 200
+            # Block replica in read()
+            $master config set rdb-key-save-delay 10000
+            # set speedy shutdown
+            $master config set save ""
+            # Start the replication process...
+            $replica replicaof $master_host $master_port
+
+            # Wait for the replica to start reading the rdb
+            set res [wait_for_log_messages -1 {"*Loading DB in memory*"} 0 200 10]
+            set loglines [lindex $res 1]
+            
+            # Wait till we see the watchgod log line AFTER the loading started
+            wait_for_log_messages -1 {"*WATCHDOG TIMER EXPIRED*"} $loglines 200 10
+            
+            # Make sure we're still loading, and that there was just one full sync attempt
+            assert ![log_file_matches [srv -1 stdout] "*Reconnecting to MASTER*"]            
+            assert_equal 1 [s 0 sync_full]
+            assert_equal 1 [s -1 loading]
+        }
+    }
+} {} {external:skip}