[Mesa-dev] [PATCH] egl/android: prevent deadlock in droid_query_buffer_age

[Min He]

To avoid blocking other EGL calls, release the display mutex before
calling update_buffers(), which will call droid_window_dequeue_buffer().
The lock appears like below:
1. Consumer thread: updateTexImage() -> updateAndReleaseLocked() ->
syncForReleaseLocked() -> eglDupNativeFenceFDANDROID() ->
_eglLockDisplay() -> waiting for the dpy lock.

2. Producer thread: eglQuerySurface() (acquired dpy lock) ->
droid_query_buffer_age() -> update_buffers() ->
android::Surface::dequeueBuffer() ->
android::BufferQueueProducer::waitForFreeSlotThenRelock()

This patch fixes some failure cases in android graphics cts test.

Signed-off-by: Min He <min.he at intel.com>
Signed-off-by: Chenglei Ren <chenglei.ren at intel.com>
Tested-by: Chenglei Ren <chenglei.ren at intel.com>
---
 src/egl/drivers/dri2/platform_android.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/egl/drivers/dri2/platform_android.c b/src/egl/drivers/dri2/platform_android.c
index 7f1a496..c6f895a 100644
--- a/src/egl/drivers/dri2/platform_android.c
+++ b/src/egl/drivers/dri2/platform_android.c
@@ -610,11 +610,18 @@ droid_query_buffer_age(_EGLDriver *drv,
 {
    struct dri2_egl_surface *dri2_surf = dri2_egl_surface(surface);
 
+   /* To avoid blocking other EGL calls, release the display mutex before
+    * we enter droid_window_dequeue_buffer() and re-acquire the mutex upon
+    * return.
+    */
+   mtx_unlock(&disp->Mutex);
    if (update_buffers(dri2_surf) < 0) {
       _eglError(EGL_BAD_ALLOC, "droid_query_buffer_age");
+      mtx_lock(&disp->Mutex);
       return -1;
    }
 
+   mtx_lock(&disp->Mutex);
    return dri2_surf->back ? dri2_surf->back->age : 0;
 }
 
-- 
2.7.4