Fix lastbgsave_status, when new child signal handler get intended kill

And add a test for that.

src/server.c

@@ -1910,6 +1910,13 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
 
             if (WIFSIGNALED(statloc)) bysignal = WTERMSIG(statloc);
 
+            /* sigKillChildHandler catches the signal and calls exit(), but we
+             * must make sure not to flag lastbgsave_status, etc incorrectly. */
+            if (exitcode == SIGUSR1) {
+                bysignal = SIGUSR1;
+                exitcode = 1;
+            }
+
             if (pid == -1) {
                 serverLog(LL_WARNING,"wait3() returned an error: %s. "
                     "rdb_child_pid = %d, aof_child_pid = %d, module_child_pid = %d",
@@ -4578,7 +4585,7 @@ static void sigKillChildHandler(int sig) {
     UNUSED(sig);
     /* this handler is needed to resolve a valgrind warning */
     serverLogFromHandler(LL_WARNING, "Received SIGUSR1 in child, exiting now.");
-    exitFromChild(1);
+    exitFromChild(SIGUSR1);
 }
 
 void setupChildSignalHandlers(void) {

tests/integration/rdb.tcl

@@ -115,3 +115,17 @@ start_server_and_kill_it [list "dir" $server_path] {
         }
     }
 }
+
+start_server {} {
+    test {Test FLUSHALL aborts bgsave} {
+        r config set rdb-key-save-delay 1000
+        r debug populate 1000
+        r bgsave
+        assert_equal [s rdb_bgsave_in_progress] 1
+        r flushall
+        after 200
+        assert_equal [s rdb_bgsave_in_progress] 0
+        # make sure the server is still writable
+        r set x xx
+    }
+}