qemu-kvm/kvm-coroutine-win32-use-QEMU_DEFINE_STATIC_CO_TLS.patch

From 336581e6e9ace3f1ddd24ad0a258db9785f9b0ed Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Tue, 17 May 2022 12:08:12 +0100
Subject: [PATCH 3/6] coroutine-win32: use QEMU_DEFINE_STATIC_CO_TLS()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
RH-MergeRequest: 89: coroutine: use coroutine TLS macros to protect thread-local variables
RH-Commit: [3/3] 55b35dfdae1bc7d6f614ac9f81a92f5c6431f713 (stefanha/centos-stream-qemu-kvm)
RH-Bugzilla: 1952483
RH-Acked-by: Hanna Reitz <hreitz@redhat.com>
RH-Acked-by: Eric Blake <eblake@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

Thread-Local Storage variables cannot be used directly from coroutine
code because the compiler may optimize TLS variable accesses across
qemu_coroutine_yield() calls. When the coroutine is re-entered from
another thread the TLS variables from the old thread must no longer be
used.

Use QEMU_DEFINE_STATIC_CO_TLS() for the current and leader variables.

I think coroutine-win32.c could get away with __thread because the
variables are only used in situations where either the stale value is
correct (current) or outside coroutine context (loading leader when
current is NULL). Due to the difficulty of being sure that this is
really safe in all scenarios it seems worth converting it anyway.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220307153853.602859-4-stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit c1fe694357a328c807ae3cc6961c19e923448fcc)
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 util/coroutine-win32.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/util/coroutine-win32.c b/util/coroutine-win32.c
index de6bd4fd3e..c02a62c896 100644
--- a/util/coroutine-win32.c
+++ b/util/coroutine-win32.c
@@ -25,6 +25,7 @@
 #include "qemu/osdep.h"
 #include "qemu-common.h"
 #include "qemu/coroutine_int.h"
+#include "qemu/coroutine-tls.h"
 
 typedef struct
 {
@@ -34,8 +35,8 @@ typedef struct
     CoroutineAction action;
 } CoroutineWin32;
 
-static __thread CoroutineWin32 leader;
-static __thread Coroutine *current;
+QEMU_DEFINE_STATIC_CO_TLS(CoroutineWin32, leader);
+QEMU_DEFINE_STATIC_CO_TLS(Coroutine *, current);
 
 /* This function is marked noinline to prevent GCC from inlining it
  * into coroutine_trampoline(). If we allow it to do that then it
@@ -52,7 +53,7 @@ qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
     CoroutineWin32 *from = DO_UPCAST(CoroutineWin32, base, from_);
     CoroutineWin32 *to = DO_UPCAST(CoroutineWin32, base, to_);
 
-    current = to_;
+    set_current(to_);
 
     to->action = action;
     SwitchToFiber(to->fiber);
@@ -89,14 +90,21 @@ void qemu_coroutine_delete(Coroutine *co_)
 
 Coroutine *qemu_coroutine_self(void)
 {
+    Coroutine *current = get_current();
+
     if (!current) {
-        current = &leader.base;
-        leader.fiber = ConvertThreadToFiber(NULL);
+        CoroutineWin32 *leader = get_ptr_leader();
+
+        current = &leader->base;
+        set_current(current);
+        leader->fiber = ConvertThreadToFiber(NULL);
     }
     return current;
 }
 
 bool qemu_in_coroutine(void)
 {
+    Coroutine *current = get_current();
+
     return current && current->caller;
 }
-- 
2.31.1