Check OOM at script start to get stable lua OOM state.

Checking OOM by `getMaxMemoryState` inside script might get different result
with `freeMemoryIfNeededAndSafe` at script start, because lua stack and
arguments also consume memory.

This leads to memory `borderline` when memory grows near server.maxmemory:

- `freeMemoryIfNeededAndSafe` at script start detects no OOM, no memory freed
- `getMaxMemoryState` inside script detects OOM, script aborted

We solve this 'borderline' issue by saving OOM state at script start to get
stable lua OOM state.

related to issue #6565 and #5250.

1 files changed, 3 insertions, 4 deletions

diff --git a/src/scripting.c b/src/scripting.c
index 9282b7fd9..5ed24ffad 100644
--- a/src/scripting.c
+++ b/src/scripting.c
@@ -655,12 +655,11 @@ int luaRedisGenericCommand(lua_State *lua, int raise_error) {
         !server.loading &&              /* Don't care about mem if loading. */
         !server.masterhost &&           /* Slave must execute the script. */
         server.lua_write_dirty == 0 &&  /* Script had no side effects so far. */
+        server.lua_oom &&               /* Detected OOM when script start. */
         (cmd->flags & CMD_DENYOOM))
     {
-        if (getMaxmemoryState(NULL,NULL,NULL,NULL) != C_OK) {
-            luaPushError(lua, shared.oomerr->ptr);
-            goto cleanup;
-        }
+        luaPushError(lua, shared.oomerr->ptr);
+        goto cleanup;
     }
 
     if (cmd->flags & CMD_RANDOM) server.lua_random_dirty = 1;