Use monotonic clock to check for Lua script timeout. (#8812)

This prevents a case where NTP moves the system clock
forward resulting in a false detection of a busy script.

Signed-off-by: zyxwvu Shi <i@shiyc.cn>

src/db.c

@@ -1480,7 +1480,7 @@ int keyIsExpired(redisDb *db, robj *key) {
      * script execution, making propagation to slaves / AOF consistent.
      * See issue #1525 on Github for more information. */
     if (server.lua_caller) {
-        now = server.lua_time_start;
+        now = server.lua_time_snapshot;
     }
     /* If we are in the middle of a command execution, we still want to use
      * a reference time that does not change: in that case we just use the

src/scripting.c

@@ -31,6 +31,7 @@
 #include "sha1.h"
 #include "rand.h"
 #include "cluster.h"
+#include "monotonic.h"
 
 #include <lua.h>
 #include <lauxlib.h>
@@ -1427,7 +1428,7 @@ sds luaCreateFunction(client *c, lua_State *lua, robj *body) {
 
 /* This is the Lua script "count" hook that we use to detect scripts timeout. */
 void luaMaskCountHook(lua_State *lua, lua_Debug *ar) {
-    long long elapsed = mstime() - server.lua_time_start;
+    long long elapsed = elapsedMs(server.lua_time_start);
     UNUSED(ar);
     UNUSED(lua);
 
@@ -1578,7 +1579,8 @@ void evalGenericCommand(client *c, int evalsha) {
     server.in_eval = 1;
     server.lua_caller = c;
     server.lua_cur_script = funcname + 2;
-    server.lua_time_start = mstime();
+    server.lua_time_start = getMonotonicUs();
+    server.lua_time_snapshot = mstime();
     server.lua_kill = 0;
     if (server.lua_time_limit > 0 && ldb.active == 0) {
         lua_sethook(lua,luaMaskCountHook,LUA_MASKCOUNT,100000);
@@ -2729,7 +2731,7 @@ void luaLdbLineHook(lua_State *lua, lua_Debug *ar) {
 
     /* Check if a timeout occurred. */
     if (ar->event == LUA_HOOKCOUNT && ldb.step == 0 && bp == 0) {
-        mstime_t elapsed = mstime() - server.lua_time_start;
+        mstime_t elapsed = elapsedMs(server.lua_time_start);
         mstime_t timelimit = server.lua_time_limit ?
                              server.lua_time_limit : 5000;
         if (elapsed >= timelimit) {
@@ -2759,6 +2761,7 @@ void luaLdbLineHook(lua_State *lua, lua_Debug *ar) {
             lua_pushstring(lua, "timeout during Lua debugging with client closing connection");
             lua_error(lua);
         }
-        server.lua_time_start = mstime();
+        server.lua_time_start = getMonotonicUs();
+        server.lua_time_snapshot = mstime();
     }
 }

src/server.h

@@ -1571,7 +1571,8 @@ struct redisServer {
     dict *lua_scripts;         /* A dictionary of SHA1 -> Lua scripts */
     unsigned long long lua_scripts_mem;  /* Cached scripts' memory + oh */
     mstime_t lua_time_limit;  /* Script timeout in milliseconds */
-    mstime_t lua_time_start;  /* Start time of script, milliseconds time */
+    monotime lua_time_start;  /* monotonic timer to detect timed-out script */
+    mstime_t lua_time_snapshot; /* Snapshot of mstime when script is started */
     int lua_write_dirty;  /* True if a write command was called during the
                              execution of the current script. */
     int lua_random_dirty; /* True if a random command was called during the