[Tarantool-patches] [PATCH] lua: avoid panic if HOOK_GC is not active

[Sergey Kaplun]

Panic at fiber.yield() occures inside any active hook.

This is the regression from 96dbc49d097a96af5273cce2b5663db5917f4ea9
('lua: prohibit fiber yield when GC hook is active').

This patch fixes false positive panic in cases when VM is not running
a GC hook.

Reported-by: Michael Filonenko <filonenko.mikhail at gmail.com>
Follows up #4727
Closes #5649
---

Branch: https://github.com/tarantool/tarantool/tree/skaplun/gh-5649-fix-for-debug-hook
Issue: https://github.com/tarantool/tarantool/issues/5649
CI: https://gitlab.com/tarantool/tarantool/-/pipelines/233249505

 src/lua/utils.c                               |  2 +-
 .../gh-5649-yield-in-debug-hook.test.lua      | 25 +++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100755 test/app-tap/gh-5649-yield-in-debug-hook.test.lua

diff --git a/src/lua/utils.c b/src/lua/utils.c
index 23fbdd4ad..b5a6ca5b7 100644
--- a/src/lua/utils.c
+++ b/src/lua/utils.c
@@ -1375,7 +1375,7 @@ void cord_on_yield(void)
 	 * earlier. As a result fiber switch is prohibited when
 	 * GC hook is active and the platform is forced to stop.
 	 */
-	if (unlikely(g->hookmask & (HOOK_ACTIVE|HOOK_GC))) {
+	if (unlikely(g->hookmask & HOOK_GC)) {
 		struct lua_State *L = fiber()->storage.lua.stack;
 		assert(L != NULL);
 		lua_pushfstring(L, "fiber %d is switched while running GC"
diff --git a/test/app-tap/gh-5649-yield-in-debug-hook.test.lua b/test/app-tap/gh-5649-yield-in-debug-hook.test.lua
new file mode 100755
index 000000000..9c1cca51f
--- /dev/null
+++ b/test/app-tap/gh-5649-yield-in-debug-hook.test.lua
@@ -0,0 +1,25 @@
+#!/usr/bin/env tarantool
+
+local fiber = require('fiber')
+local tap = require('tap')
+local test = tap.test('yield-in-debug-hook')
+
+test:plan(2)
+
+-- Test that HOOK_ACTIVE is not enough to panic and
+-- fiber still can use general hooks at switches.
+fiber.create(function()
+  local old_hook, mask, count = debug.gethook()
+  debug.sethook(function()
+    fiber.yield()
+  end, 'c')
+  -- All ok if panic doesn't occure.
+  -- Yield before hook is set back.
+  debug.sethook(old_hook, mask, count)
+  test:ok(true)
+end)
+-- Return to second fiber.
+fiber.yield()
+test:ok(true)
+
+os.exit(test:check() and 0 or 1)
-- 
2.28.0