r300g: fix a possible race when counting contexts

Atomics aren't sufficient here.

3 files changed, 8 insertions, 2 deletions

diff --git a/src/gallium/drivers/r300/r300_context.c b/src/gallium/drivers/r300/r300_context.c
index a89bf7fac31..da6b0bb8aa7 100644
--- a/src/gallium/drivers/r300/r300_context.c
+++ b/src/gallium/drivers/r300/r300_context.c
@@ -38,19 +38,21 @@
 static void r300_update_num_contexts(struct r300_screen *r300screen,
                                      int diff)
 {
+    pipe_mutex_lock(r300screen->num_contexts_mutex);
     if (diff > 0) {
-        p_atomic_inc(&r300screen->num_contexts);
+        r300screen->num_contexts++;
 
         if (r300screen->num_contexts > 1)
             util_slab_set_thread_safety(&r300screen->pool_buffers,
                                         UTIL_SLAB_MULTITHREADED);
     } else {
-        p_atomic_dec(&r300screen->num_contexts);
+        r300screen->num_contexts--;
 
         if (r300screen->num_contexts <= 1)
             util_slab_set_thread_safety(&r300screen->pool_buffers,
                                         UTIL_SLAB_SINGLETHREADED);
     }
+    pipe_mutex_unlock(r300screen->num_contexts_mutex);
 }
 
 static void r300_release_referenced_objects(struct r300_context *r300)
diff --git a/src/gallium/drivers/r300/r300_screen.c b/src/gallium/drivers/r300/r300_screen.c
index ed47315f42d..77a9c6ad86f 100644
--- a/src/gallium/drivers/r300/r300_screen.c
+++ b/src/gallium/drivers/r300/r300_screen.c
@@ -398,6 +398,7 @@ static void r300_destroy_screen(struct pipe_screen* pscreen)
     struct r300_winsys_screen *rws = r300_winsys_screen(pscreen);
 
     util_slab_destroy(&r300screen->pool_buffers);
+    pipe_mutex_destroy(r300screen->num_contexts_mutex);
 
     if (rws)
       rws->destroy(rws);
@@ -459,6 +460,8 @@ struct pipe_screen* r300_screen_create(struct r300_winsys_screen *rws)
             r300screen->caps.is_r500 &&
             rws->get_value(rws, R300_VID_DRM_2_3_0);
 
+    pipe_mutex_init(r300screen->num_contexts_mutex);
+
     util_slab_create(&r300screen->pool_buffers,
                      sizeof(struct r300_resource), 64,
                      UTIL_SLAB_SINGLETHREADED);
diff --git a/src/gallium/drivers/r300/r300_screen.h b/src/gallium/drivers/r300/r300_screen.h
index c935f55ccbf..576f9c1f4a9 100644
--- a/src/gallium/drivers/r300/r300_screen.h
+++ b/src/gallium/drivers/r300/r300_screen.h
@@ -52,6 +52,7 @@ struct r300_screen {
     /* The number of created contexts to know whether we have multiple
      * contexts or not. */
     int num_contexts;
+    pipe_mutex num_contexts_mutex;
 };