[Qemu-devel] [PATCH] block: Fix race in gluster_finish_aiocb

[Asias He <asias@redhat.com>]

In block/gluster.c, we have

gluster_finish_aiocb
{
   if (retval != sizeof(acb)) {
      qemu_mutex_lock_iothread(); /* We are in gluster thread context */
      ...
      qemu_mutex_unlock_iothread();
   }
}

qemu tools, e.g. qemu-img, might race here because
qemu_mutex_{lock,unlock}_iothread are a nop operation and
gluster_finish_aiocb is in the gluster thread context.

To fix, we introduce our own mutex for qemu tools.

Signed-off-by: Asias He <asias@redhat.com>
---
 stubs/iothread-lock.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/stubs/iothread-lock.c b/stubs/iothread-lock.c
index 5d8aca1..d5c6dec 100644
--- a/stubs/iothread-lock.c
+++ b/stubs/iothread-lock.c
@@ -1,10 +1,21 @@
 #include "qemu-common.h"
 #include "qemu/main-loop.h"
 
+static QemuMutex qemu_tools_mutex;
+static pthread_once_t qemu_tools_once = PTHREAD_ONCE_INIT;
+
+static void qemu_tools_mutex_init(void)
+{
+    qemu_mutex_init(&qemu_tools_mutex);
+}
+
 void qemu_mutex_lock_iothread(void)
 {
+    pthread_once(&qemu_tools_once, qemu_tools_mutex_init);
+    qemu_mutex_lock(&qemu_tools_mutex);
 }
 
 void qemu_mutex_unlock_iothread(void)
 {
+    qemu_mutex_unlock(&qemu_tools_mutex);
 }
-- 
1.8.3.1