Fix fork done handler wrongly update fsync metrics and enhance AOF_FS…

…YNC_ALWAYS

This PR fix two bugs:

1. About the MP-AOF one, that code assumes that we started a new AOF file just
now (when we have a new base into which we're gonna incrementally write), but the
fact is that with multipart-aof, the fork done handler doesn't really affect the
incremental file being maintained by the parent process, there's no reason to re-issue
SELECT, and i suppose there's no reason to update any of the fsync metrics.
This should have been deleted with MP-AOF (introduced in redis#9788, 7.0).
The aof_fsync_offset it updates will cause us to miss an fsync in flushAppendOnlyFile,
if we stop write commands in AOF_FSYNC_EVERYSEC

2. About the AOF_FSYNC_ALWAYS one, it is follow redis#6053 (the details is in redis#5985),
we also check AOF_FSYNC_ALWAYS to prevent users from switching from everysec to always.

We detected these problems with WAITAOF test (redis 7.2), introduced in redis#11713.

src/aof.c

@@ -1087,6 +1087,15 @@ void flushAppendOnlyFile(int force) {
             server.unixtime > server.aof_last_fsync &&
             !(sync_in_progress = aofFsyncInProgress())) {
             goto try_fsync;
+
+        /* Check if we need to do fsync even the aof buffer is empty,
+         * the reason is described in the previous AOF_FSYNC_EVERYSEC if,
+         * and AOF_FSYNC_ALWAYS is also checked here to prevent users from
+         * changing the aof_fsync from everysec to always.  */
+        } else if (server.aof_fsync == AOF_FSYNC_ALWAYS &&
+                   server.aof_fsync_offset != server.aof_current_size)
+        {
+            goto try_fsync;
         } else {
             return;
         }
@@ -2666,15 +2675,6 @@ void backgroundRewriteDoneHandler(int exitcode, int bysignal) {
         /* We can safely let `server.aof_manifest` point to 'temp_am' and free the previous one. */
         aofManifestFreeAndUpdate(temp_am);
 
-        if (server.aof_fd != -1) {
-            /* AOF enabled. */
-            server.aof_selected_db = -1; /* Make sure SELECT is re-issued */
-            server.aof_current_size = getAppendOnlyFileSize(new_base_filename, NULL) + server.aof_last_incr_size;
-            server.aof_rewrite_base_size = server.aof_current_size;
-            server.aof_fsync_offset = server.aof_current_size;
-            server.aof_last_fsync = server.unixtime;
-        }
-
         /* We don't care about the return value of `aofDelHistoryFiles`, because the history
          * deletion failure will not cause any problems. */
         aofDelHistoryFiles();

tests/unit/wait.tcl

@@ -175,10 +175,39 @@ tags {"wait aof network external:skip"} {
             $replica config set appendfsync everysec
 
             test {WAITAOF replica copy everysec} {
+                $replica config set appendfsync everysec
+                waitForBgrewriteaof $replica ;# Make sure there is no AOFRW
+
                 $master incr foo
                 assert_equal [$master waitaof 0 1 0] {1 1}
             }
 
+            test {WAITAOF replica copy everysec with AOFRW} {
+                $replica config set appendfsync everysec
+
+                # Need an AOFRW that can be done in a second.
+                $replica bgrewriteaof
+
+                $master incr foo
+                assert_equal [$master waitaof 0 1 0] {1 1}
+            }
+
+            test {WAITAOF replica copy everysec->always with AOFRW} {
+                $replica config set appendfsync everysec
+
+                waitForBgrewriteaof $replica
+
+                # Need an AOFRW that can be done in a second.
+                $replica bgrewriteaof
+
+                $master incr foo
+
+                # Change appendfsync from everysec to always
+                $replica config set appendfsync always
+
+                assert_equal [$master waitaof 0 1 0] {1 1}
+            }
+
             test {WAITAOF replica copy appendfsync always} {
                 $replica config set appendfsync always
                 $master incr foo