From c1fe694357a328c807ae3cc6961c19e923448fcc Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Mon, 7 Mar 2022 15:38:53 +0000 Subject: [PATCH] coroutine-win32: use QEMU_DEFINE_STATIC_CO_TLS() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Message-Id: <20220307153853.602859-4-stefanha@redhat.com> Reviewed-by: Philippe Mathieu-Daudé Signed-off-by: Kevin Wolf --- 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 c196f956d2..7db2e8f8c8 100644 --- a/util/coroutine-win32.c +++ b/util/coroutine-win32.c @@ -24,6 +24,7 @@ #include "qemu/osdep.h" #include "qemu/coroutine_int.h" +#include "qemu/coroutine-tls.h" typedef struct { @@ -33,8 +34,8 @@ 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 @@ -51,7 +52,7 @@ 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); @@ -88,14 +89,21 @@ 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; }