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TASK-209191 block global trace while inheriting thread data #12

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TASK-209191 block global trace while inheriting thread data #12

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6b2bd56
TASK-209191 block global trace while inheriting thread data
balupillai Mar 4, 2026
b88bfd0
TASK-209191 fix lock ordering
balupillai Mar 4, 2026
a21ce84
TASK-209191 lock the lua thread while inherit
balupillai Mar 6, 2026
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12 changes: 12 additions & 0 deletions src/lgc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1624,16 +1624,24 @@ void luaC_inherit_thread(lua_State *L, lua_State *th)
{
int i;
GCheader *steal, *tmp;
thr_State *pt;

lua_lock(th);
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@cursor cursor bot Mar 6, 2026

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Double-locking th causes deadlock with existing callers

High Severity

The newly added lua_lock(th) inside luaC_inherit_thread double-locks th because at least two call sites already hold that lock. In reclaim_object (lgc.c), the caller does lua_lock(th) before calling luaC_inherit_thread(L, th). In lua_delrefthread (lapi.c), lua_lock(L) is called on the source thread which becomes the th parameter. If lua_lock is a non-recursive mutex, this will deadlock.

Additional Locations (1)

Fix in Cursor Fix in Web


if (th->heap == NULL) {
// already done
lua_unlock(th);
return;
}

pt = luaC_get_per_thread(L);

/* when a thread is reclaimed, the executing thread
* needs to steal its contents */
lock_all_threads();

block_collector(L, pt);

if (TEST_INHERIT_THREAD_DELAY_MS > 0) {
/* TR-1945: Both global trace and thread delref will grab
* the "all threads" lock. To induce false contention on that lock
Expand Down Expand Up @@ -1671,11 +1679,15 @@ void luaC_inherit_thread(lua_State *L, lua_State *th)
make_grey(L, steal);
}
TAILQ_REMOVE(&G(L)->all_heaps, th->heap, heaps);
unblock_collector(L, pt);

unlock_all_threads();

free(th->heap);
th->heap = NULL;

lua_unlock(th);

ck_pr_inc_32(&G(L)->need_global_trace);
}

Expand Down