From 7866e124a852c344b5762eb917c03a1f95d9058d Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Wed, 30 Apr 2025 14:17:48 -0700
Subject: [PATCH] Use rb_current_ec_noinline in assertions

When doing a coroutine transfer from one thread to another, there's a
risk that the compiler will reuse an address from TLS before the
transfer to the new thread.

These VM assertions are all in places we would not otherwise be reading
from TLS, but using the value of `ec` or `cr` passed in. Switching these
to test against rb_current_ec_noinline() instead ensures there isn't an
optimization applied to how we read ruby_current_ec.

Currently it seems we were hitting this on LLVM 18 specifically, but I
don't know of any reason other versions wouldn't have the same issue.
---
 ractor.c  | 10 ++++++----
 vm_core.h |  2 +-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/ractor.c b/ractor.c
index d50704dec4..bdff0c99fd 100644
--- a/ractor.c
+++ b/ractor.c
@@ -39,7 +39,8 @@ static void
 ASSERT_ractor_unlocking(rb_ractor_t *r)
 {
 #if RACTOR_CHECK_MODE > 0
-    if (rb_current_execution_context(false) != NULL && r->sync.locked_by == rb_ractor_self(GET_RACTOR())) {
+    const rb_execution_context_t *ec = rb_current_ec_noinline();
+    if (ec != NULL && r->sync.locked_by == rb_ractor_self(rb_ec_ractor_ptr(ec))) {
         rb_bug("recursive ractor locking");
     }
 #endif
@@ -49,7 +50,8 @@ static void
 ASSERT_ractor_locking(rb_ractor_t *r)
 {
 #if RACTOR_CHECK_MODE > 0
-    if (rb_current_execution_context(false) != NULL && r->sync.locked_by != rb_ractor_self(GET_RACTOR())) {
+    const rb_execution_context_t *ec = rb_current_ec_noinline();
+    if (ec != NULL && r->sync.locked_by != rb_ractor_self(rb_ec_ractor_ptr(ec))) {
         rp(r->sync.locked_by);
         rb_bug("ractor lock is not acquired.");
     }
@@ -77,7 +79,7 @@ ractor_lock(rb_ractor_t *r, const char *file, int line)
 static void
 ractor_lock_self(rb_ractor_t *cr, const char *file, int line)
 {
-    VM_ASSERT(cr == GET_RACTOR());
+    VM_ASSERT(cr == rb_ec_ractor_ptr(rb_current_ec_noinline()));
 #if RACTOR_CHECK_MODE > 0
     VM_ASSERT(cr->sync.locked_by != cr->pub.self);
 #endif
@@ -99,7 +101,7 @@ ractor_unlock(rb_ractor_t *r, const char *file, int line)
 static void
 ractor_unlock_self(rb_ractor_t *cr, const char *file, int line)
 {
-    VM_ASSERT(cr == GET_RACTOR());
+    VM_ASSERT(cr == rb_ec_ractor_ptr(rb_current_ec_noinline()));
 #if RACTOR_CHECK_MODE > 0
     VM_ASSERT(cr->sync.locked_by == cr->pub.self);
 #endif
diff --git a/vm_core.h b/vm_core.h
index a9bd47aaae..37af34df9c 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -2118,7 +2118,7 @@ rb_vm_check_ints(rb_execution_context_t *ec)
     VM_ASSERT(ruby_assert_critical_section_entered == 0);
 #endif
 
-    VM_ASSERT(ec == GET_EC());
+    VM_ASSERT(ec == rb_current_ec_noinline());
 
     if (UNLIKELY(RUBY_VM_INTERRUPTED_ANY(ec))) {
         rb_threadptr_execute_interrupts(rb_ec_thread_ptr(ec), 0);