From ffbd90e5f4eba620c7cd631b04f0ed31beb22ffa Mon Sep 17 00:00:00 2001

From: Stefan Hajnoczi <stefanha@redhat.com>

Date: Tue, 17 May 2022 12:07:56 +0100

Subject: [PATCH 1/6] coroutine-ucontext: 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: [1/3] a9782fe8e919c4bd317b7e8744c7ff57d898add3 (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.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Message-Id: <20220307153853.602859-2-stefanha@redhat.com>

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

(cherry picked from commit 34145a307d849d0b6734d0222a7aa0bb9eef7407)

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

---

 util/coroutine-ucontext.c | 38 ++++++++++++++++++++++++--------------

 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c

index 904b375192..127d5a13c8 100644

--- a/util/coroutine-ucontext.c

+++ b/util/coroutine-ucontext.c

@@ -25,6 +25,7 @@

 #include "qemu/osdep.h"

 #include <ucontext.h>

 #include "qemu/coroutine_int.h"

+#include "qemu/coroutine-tls.h"

 #ifdef CONFIG_VALGRIND_H

 #include <valgrind/valgrind.h>

@@ -66,8 +67,8 @@ typedef struct {

 /**

  * Per-thread coroutine bookkeeping

  */

-static __thread CoroutineUContext leader;

-static __thread Coroutine *current;

+QEMU_DEFINE_STATIC_CO_TLS(Coroutine *, current);

+QEMU_DEFINE_STATIC_CO_TLS(CoroutineUContext, leader);

 /*

  * va_args to makecontext() must be type 'int', so passing

@@ -97,14 +98,15 @@ static inline __attribute__((always_inline))

 void finish_switch_fiber(void *fake_stack_save)

 {

 #ifdef CONFIG_ASAN

+    CoroutineUContext *leaderp = get_ptr_leader();

     const void *bottom_old;

     size_t size_old;

     __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);

-    if (!leader.stack) {

-        leader.stack = (void *)bottom_old;

-        leader.stack_size = size_old;

+    if (!leaderp->stack) {

+        leaderp->stack = (void *)bottom_old;

+        leaderp->stack_size = size_old;

     }

 #endif

 #ifdef CONFIG_TSAN

@@ -161,8 +163,10 @@ static void coroutine_trampoline(int i0, int i1)

     /* Initialize longjmp environment and switch back the caller */

     if (!sigsetjmp(self->env, 0)) {

-        start_switch_fiber_asan(COROUTINE_YIELD, &fake_stack_save, leader.stack,

-                                leader.stack_size);

+        CoroutineUContext *leaderp = get_ptr_leader();

+

+        start_switch_fiber_asan(COROUTINE_YIELD, &fake_stack_save,

+                                leaderp->stack, leaderp->stack_size);

         start_switch_fiber_tsan(&fake_stack_save, self, true); /* true=caller */

         siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);

     }

@@ -297,7 +301,7 @@ qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,

     int ret;

     void *fake_stack_save = NULL;

-    current = to_;

+    set_current(to_);

     ret = sigsetjmp(from->env, 0);

     if (ret == 0) {

@@ -315,18 +319,24 @@ qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,

 Coroutine *qemu_coroutine_self(void)

 {

-    if (!current) {

-        current = &leader.base;

+    Coroutine *self = get_current();

+    CoroutineUContext *leaderp = get_ptr_leader();

+

+    if (!self) {

+        self = &leaderp->base;

+        set_current(self);

     }

 #ifdef CONFIG_TSAN

-    if (!leader.tsan_co_fiber) {

-        leader.tsan_co_fiber = __tsan_get_current_fiber();

+    if (!leaderp->tsan_co_fiber) {

+        leaderp->tsan_co_fiber = __tsan_get_current_fiber();

     }

 #endif

-    return current;

+    return self;

 }

 bool qemu_in_coroutine(void)

 {

-    return current && current->caller;

+    Coroutine *self = get_current();

+

+    return self && self->caller;

 }

-- 

2.31.1