[Mesa-dev] [PATCH] glsl: Add locking to builtin_builder singleton

[Daniel Kurtz]

Consider a multithreaded program with two contexts A and B, and the
following scenario:

1. Context A calls initialize(), which allocates mem_ctx and starts
   building built-ins.
2. Context B calls initialize(), which sees mem_ctx != NULL and assumes
   everything is already set up.  It returns.
3. Context B calls find(), which fails to find the built-in since it
   hasn't been created yet.
4. Context A finally finishes initializing the built-ins.

This will break at step 3.  Adding a lock ensures that subsequent
callers of initialize() will wait until initialization is actually
complete.

Similarly, if any thread calls release while another thread is still
initializing, or calling find(), the mem_ctx/shader would get free'd while
from under it, leading to corruption or use-after-free crashes.

Fixes sporadic failures in Piglit's glx-multithread-shader-compile as
reported in:
https://bugs.freedesktop.org/69200

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
Signed-off-by: Daniel Kurtz <djkurtz at chromium.org>
---
 src/glsl/builtin_functions.cpp | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/glsl/builtin_functions.cpp b/src/glsl/builtin_functions.cpp
index aeb8e5d..2162baa 100644
--- a/src/glsl/builtin_functions.cpp
+++ b/src/glsl/builtin_functions.cpp
@@ -4100,6 +4100,7 @@ builtin_builder::_mid3(const glsl_type *type)
 
 /* The singleton instance of builtin_builder. */
 static builtin_builder builtins;
+_glthread_DECLARE_STATIC_MUTEX(builtins_lock);
 
 /**
  * External API (exposing the built-in module to the rest of the compiler):
@@ -4108,20 +4109,28 @@ static builtin_builder builtins;
 void
 _mesa_glsl_initialize_builtin_functions()
 {
+   _glthread_LOCK_MUTEX(builtins_lock);
    builtins.initialize();
+   _glthread_UNLOCK_MUTEX(builtins_lock);
 }
 
 void
 _mesa_glsl_release_builtin_functions()
 {
+   _glthread_LOCK_MUTEX(builtins_lock);
    builtins.release();
+   _glthread_UNLOCK_MUTEX(builtins_lock);
 }
 
 ir_function_signature *
 _mesa_glsl_find_builtin_function(_mesa_glsl_parse_state *state,
                                  const char *name, exec_list *actual_parameters)
 {
-   return builtins.find(state, name, actual_parameters);
+   ir_function_signature * s;
+   _glthread_LOCK_MUTEX(builtins_lock);
+   s = builtins.find(state, name, actual_parameters);
+   _glthread_UNLOCK_MUTEX(builtins_lock);
+   return s;
 }
 
 gl_shader *
-- 
1.9.0.rc1.175.g0b1dcb5