From 1b0f943da7dfb25987456a77259edbeea0b94edc Mon Sep 17 00:00:00 2001 From: Roberto Ierusalimschy 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}