mesa: Fix locking of GLsync objects.

GLsync objects had a race condition when used from multiple threads
(which is the main point of the extension, really); it could be
validated as a sync object at the beginning of the function, and then
deleted by another thread before use, causing crashes. Fix this by
changing all casts from GLsync to struct gl_sync_object to a new
function _mesa_get_and_ref_sync() that validates and increases
the refcount.

In a similar vein, validation itself uses _mesa_set_search(), which
requires synchronization -- it was called without a mutex held, causing
spurious error returns and other issues. Since _mesa_get_and_ref_sync()
now takes the shared context mutex, this problem is also resolved.

Fixes bug #92757, found while developing Nageru, my live video mixer
(due for release at FOSDEM 2016).

v2: Marek: silence warnings, fix declaration after code

Signed-off-by: Steinar H. Gunderson <[email protected]>
Cc: "11.0 11.1" <[email protected]>
Signed-off-by: Marek Olšák <[email protected]>

1 files changed, 4 insertions, 7 deletions

diff --git a/src/mesa/main/syncobj.h b/src/mesa/main/syncobj.h
index 5d510e873a9..ea4a71222c0 100644
--- a/src/mesa/main/syncobj.h
+++ b/src/mesa/main/syncobj.h
@@ -47,15 +47,12 @@ _mesa_init_sync(struct gl_context *);
 extern void
 _mesa_free_sync_data(struct gl_context *);
 
-extern void
-_mesa_ref_sync_object(struct gl_context *ctx, struct gl_sync_object *syncObj);
+struct gl_sync_object *
+_mesa_get_and_ref_sync(struct gl_context *ctx, GLsync sync, bool incRefCount);
 
 extern void
-_mesa_unref_sync_object(struct gl_context *ctx, struct gl_sync_object *syncObj);
-
-extern bool
-_mesa_validate_sync(struct gl_context *ctx,
-                    const struct gl_sync_object *syncObj);
+_mesa_unref_sync_object(struct gl_context *ctx, struct gl_sync_object *syncObj,
+                        int amount);
 
 extern GLboolean GLAPIENTRY
 _mesa_IsSync(GLsync sync);