[Qemu-devel] [PATCH v2] vnc: threaded server depends on io-thread

[Corentin Chary <corentin.chary@gmail.com>]

The threaded VNC servers messed up with QEMU fd handlers without
any kind of locking, and that can cause some nasty race conditions.

The IO-Thread provides appropriate locking primitives to avoid that.
This patch makes CONFIG_VNC_THREAD depends on CONFIG_IO_THREAD,
and add lock and unlock calls around the two faulty calls.

Thanks to Jan Kiszka for helping me solve this issue.

Cc: Jan Kiszka <jan.kiszka@web.de>
Signed-off-by: Corentin Chary <corentin.chary@gmail.com>
---
The previous patch was total crap, introduced race conditions,
and probably crashs on client disconnections.

 configure           |    9 +++++++++
 ui/vnc-jobs-async.c |   24 +++++++++++++++++++-----
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/configure b/configure
index 5513d3e..c8c1ac1 100755
--- a/configure
+++ b/configure
@@ -2455,6 +2455,15 @@ if test \( "$cpu" = "i386" -o "$cpu" = "x86_64" \) -a \
   roms="optionrom"
 fi
 
+# VNC Thread depends on IO Thread
+if test "$vnc_thread" = "yes" -a "$io_thread" != "yes"; then
+  echo
+  echo "ERROR: VNC thread depends on IO thread which isn't enabled."
+  echo "Please use --enable-io-thread if you want to enable it."
+  echo
+  exit 1
+fi
+
 
 echo "Install prefix    $prefix"
 echo "BIOS directory    `eval echo $datadir`"
diff --git a/ui/vnc-jobs-async.c b/ui/vnc-jobs-async.c
index f596247..d0c6f61 100644
--- a/ui/vnc-jobs-async.c
+++ b/ui/vnc-jobs-async.c
@@ -190,6 +190,18 @@ static void vnc_async_encoding_end(VncState *orig, VncState *local)
     queue->buffer = local->output;
 }
 
+static void vnc_worker_lock_output(VncState *vs)
+{
+    qemu_mutex_lock_iothread();
+    vnc_lock_output(vs);
+}
+
+static void vnc_worker_unlock_output(VncState *vs)
+{
+    vnc_unlock_output(vs);
+    qemu_mutex_unlock_iothread();
+}
+
 static int vnc_worker_thread_loop(VncJobQueue *queue)
 {
     VncJob *job;
@@ -211,11 +223,11 @@ static int vnc_worker_thread_loop(VncJobQueue *queue)
         return -1;
     }
 
-    vnc_lock_output(job->vs);
+    vnc_worker_lock_output(job->vs);
     if (job->vs->csock == -1 || job->vs->abort == true) {
         goto disconnected;
     }
-    vnc_unlock_output(job->vs);
+    vnc_worker_unlock_output(job->vs);
 
     /* Make a local copy of vs and switch output buffers */
     vnc_async_encoding_start(job->vs, &vs);
@@ -236,7 +248,7 @@ static int vnc_worker_thread_loop(VncJobQueue *queue)
             /* output mutex must be locked before going to
              * disconnected:
              */
-            vnc_lock_output(job->vs);
+            vnc_worker_lock_output(job->vs);
             goto disconnected;
         }
 
@@ -255,7 +267,7 @@ static int vnc_worker_thread_loop(VncJobQueue *queue)
     vs.output.buffer[saved_offset + 1] = n_rectangles & 0xFF;
 
     /* Switch back buffers */
-    vnc_lock_output(job->vs);
+    vnc_worker_lock_output(job->vs);
     if (job->vs->csock == -1) {
         goto disconnected;
     }
@@ -266,10 +278,12 @@ disconnected:
     /* Copy persistent encoding data */
     vnc_async_encoding_end(job->vs, &vs);
     flush = (job->vs->csock != -1 && job->vs->abort != true);
-    vnc_unlock_output(job->vs);
+    vnc_worker_unlock_output(job->vs);
 
     if (flush) {
+        qemu_mutex_lock_iothread();
         vnc_flush(job->vs);
+        qemu_mutex_unlock_iothread();
     }
 
     vnc_lock_queue(queue);
-- 
1.7.3.4