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, 1 insertions, 1 deletions

diff --git a/src/mesa/main/shared.c b/src/mesa/main/shared.c
index c37b31d1753..b9f7bb65fb6 100644
--- a/src/mesa/main/shared.c
+++ b/src/mesa/main/shared.c
@@ -338,7 +338,7 @@ free_shared_state(struct gl_context *ctx, struct gl_shared_state *shared)
       struct set_entry *entry;
 
       set_foreach(shared->SyncObjects, entry) {
-         _mesa_unref_sync_object(ctx, (struct gl_sync_object *) entry->key);
+         _mesa_unref_sync_object(ctx, (struct gl_sync_object *) entry->key, 1);
       }
    }
    _mesa_set_destroy(shared->SyncObjects, NULL);