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()

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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