[Qemu-devel] [PATCH v2] thread-win32: fix GetThreadContext() permanently fails

[Zavadovsky Yan <zavadovsky.yan@gmail.com>]

Calling SuspendThread() is not enough to suspend Win32 thread.
We need to call GetThreadContext() after SuspendThread()
to make sure that OS have really suspended target thread.
But GetThreadContext() needs for THREAD_GET_CONTEXT
access right on thread object.
More info about this technique can be found here:
http://blogs.msdn.com/b/oldnewthing/archive/2015/02/05/10591215.aspx

This patch adds THREAD_GET_CONTEXT to OpenThread() arguments
and change oddity 'while(GetThreadContext() == SUCCESS)' to
'if(GetThreadContext() == FAILED){exit(1);}'.
So this block of code will continue only after successful
grabbing of thread context(i.e. when thread is really suspended).
And halts otherwise with more verbose error message than previous.

Signed-off-by: Zavadovsky Yan <zavadovsky.yan@gmail.com>
---
 cpus.c                   | 14 ++++++++------
 util/qemu-thread-win32.c |  4 ++--
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/cpus.c b/cpus.c
index 4f0e54d..0df6a7d 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1089,8 +1089,8 @@ static void qemu_cpu_kick_thread(CPUState *cpu)
         CONTEXT tcgContext;
 
         if (SuspendThread(cpu->hThread) == (DWORD)-1) {
-            fprintf(stderr, "qemu:%s: GetLastError:%lu\n", __func__,
-                    GetLastError());
+            fprintf(stderr, "qemu:%s: SuspendThread GetLastError:%lu\n",
+                    __func__, GetLastError());
             exit(1);
         }
 
@@ -1098,15 +1098,17 @@ static void qemu_cpu_kick_thread(CPUState *cpu)
          * suspended until we can get the context.
          */
         tcgContext.ContextFlags = CONTEXT_CONTROL;
-        while (GetThreadContext(cpu->hThread, &tcgContext) != 0) {
-            continue;
+        if (GetThreadContext(cpu->hThread, &tcgContext) == 0) {
+            fprintf(stderr, "qemu:%s: GetThreadContext GetLastError:%lu\n",
+                    __func__, GetLastError());
+            exit(1);
         }
 
         cpu_signal(0);
 
         if (ResumeThread(cpu->hThread) == (DWORD)-1) {
-            fprintf(stderr, "qemu:%s: GetLastError:%lu\n", __func__,
-                    GetLastError());
+            fprintf(stderr, "qemu:%s: ResumeThread GetLastError:%lu\n",
+                    __func__, GetLastError());
             exit(1);
         }
     }
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index 406b52f..823eca1 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -406,8 +406,8 @@ HANDLE qemu_thread_get_handle(QemuThread *thread)
 
     EnterCriticalSection(&data->cs);
     if (!data->exited) {
-        handle = OpenThread(SYNCHRONIZE | THREAD_SUSPEND_RESUME, FALSE,
-                            thread->tid);
+        handle = OpenThread(SYNCHRONIZE | THREAD_SUSPEND_RESUME | THREAD_GET_CONTEXT,
+                            FALSE, thread->tid);
     } else {
         handle = NULL;
     }
-- 
2.4.4.windows.2