lua54/upstream1.patch

From 1b0f943da7dfb25987456a77259edbeea0b94edc Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Mon, 16 Jun 2025 16:33:02 -0300
Subject: [PATCH] Bug: new metatable in weak table can fool the GC

All-weak tables are not being revisited after being visited during
propagation; if it gets a new metatable after that, the new metatable
may not be marked.
---
 lgc.c         |  8 ++++++--
 testes/gc.lua | 10 ++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/lgc.c b/lgc.c
index 5817f9eec3..c01660abc5 100644
--- a/src/lgc.c
+++ b/src/lgc.c
@@ -553,8 +553,12 @@ static lu_mem traversetable (global_State *g, Table *h) {
       traverseweakvalue(g, h);
     else if (!weakvalue)  /* strong values? */
       traverseephemeron(g, h, 0);
-    else  /* all weak */
-      linkgclist(h, g->allweak);  /* nothing to traverse now */
+    else {  /* all weak */
+      if (g->gcstate == GCSpropagate)
+        linkgclist(h, g->grayagain);  /* must visit again its metatable */
+      else
+        linkgclist(h, g->allweak);  /* must clear collected entries */
+    }
   }
   else  /* not weak */
     traversestrongtable(g, h);
diff --git a/testes/gc.lua b/testes/gc.lua
index 03093e34ff..f017f33056 100644
--- a/testes/gc.lua
+++ b/testes/gc.lua
@@ -301,6 +301,16 @@ collectgarbage()
 assert(next(a) == string.rep('$', 11))
 
 
+if T then   -- bug since 5.3: all-weak tables are not being revisited
+  T.gcstate("propagate")
+  local t = setmetatable({}, {__mode = "kv"})
+  T.gcstate("atomic")   -- 't' was visited
+  setmetatable(t, {__mode = "kv"})
+  T.gcstate("pause")  -- its new metatable is not being visited
+  assert(getmetatable(t).__mode == "kv")
+end
+
+
 -- 'bug' in 5.1
 a = {}
 local t = {x = 10}