[Mesa-dev] [PATCH 1/2] gallivm: Allow drivers and state trackers to initialize gallivm LLVM targets

[Tom Stellard]

Drivers and state trackers that use LLVM for generating code, must
register the targets they use with LLVM's global TargetRegistry.
The TargetRegistry is not thread-safe, so all targets must be added
to the registry before it can be queried for target information.

When drivers and state trackers initialize their own targets, they need
a way to force gallivm to initialize its targets at the same time.
Otherwise, there can be a race condition in some multi-threaded
applications (e.g. glx-multihreaded-shader-compile in piglit),
when one thread creates a context for a driver that uses LLVM (e.g.
radeonsi) and another thread creates a gallivm context (glxContextCreate
does this).

The race happens when the driver thread initializes its LLVM targets and
then starts using the registry before the gallivm thread has a chance to
register its targets.

This patch allows users to force gallivm to register its targets by
adding two new functions:  gallivm_llvm_init_begin() which locks a mutex
guarding the TargetRegistry and initializes the gallivm targets, and
gallivm_llvm_init_end() which unlocks the mutex.

Drivers and state trackers should use this sequence to correctly
initialize the LLVM targets they use:

gallivm_init_llvm_begin();
LLVMInitializeFooTarget();
gallivm_init_llvm_end();

CC: "10.6 11.0" <mesa-stable at lists.freedesktop.org>
---
 src/gallium/auxiliary/gallivm/lp_bld_misc.cpp | 68 ++++++++++++++++++++++++---
 src/gallium/auxiliary/gallivm/lp_bld_misc.h   |  5 ++
 2 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
index 5e25819..8bf833e 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
+++ b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
@@ -81,6 +81,7 @@
 #  pragma pop_macro("DEBUG")
 #endif
 
+#include "os/os_thread.h"
 #include "pipe/p_config.h"
 #include "util/u_debug.h"
 #include "util/u_cpu_detect.h"
@@ -101,6 +102,64 @@ public:
 
 static LLVMEnsureMultithreaded lLVMEnsureMultithreaded;
 
+struct LLVMRegistryLock {
+private:
+   pipe_mutex mutex;
+
+public:
+   LLVMRegistryLock()
+   {
+      pipe_mutex_init(mutex);
+   }
+
+   void lock()
+   {
+      pipe_mutex_lock(mutex);
+   }
+
+   void unlock()
+   {
+      pipe_mutex_unlock(mutex);
+   }
+};
+
+static LLVMRegistryLock gallivm_llvm_registry_lock;
+
+}
+
+/**
+ * The llvm target registry is not thread-safe, so drivers and state-trackers
+ * that want to initialize targets should use the gallivm_init_llvm_begin() and
+ * gallivm_init_llvm_end() functions to safely initialize targets.  For example:
+ *
+ * gallivm_init_llvm_begin();
+ * LLVMInitializeFooTarget();
+ * gallivm_init_llvm_end();
+ *
+ * LLVM targets should be initialized before the driver tries to access the
+ * registry.
+ */
+extern "C" void
+gallivm_init_llvm_begin(void)
+{
+   static int init = 0;
+   gallivm_llvm_registry_lock.lock();
+   if (!init) {
+      // If we have a native target, initialize it to ensure it is linked in and
+      // usable by the JIT.
+      llvm::InitializeNativeTarget();
+
+      llvm::InitializeNativeTargetAsmPrinter();
+
+      llvm::InitializeNativeTargetDisassembler();
+      init = 1;
+    }
+}
+
+extern "C" void
+gallivm_init_llvm_end(void)
+{
+   gallivm_llvm_registry_lock.unlock();
 }
 
 extern "C" void
@@ -115,13 +174,8 @@ lp_set_target_options(void)
    llvm::DisablePrettyStackTrace = true;
 #endif
 
-   // If we have a native target, initialize it to ensure it is linked in and
-   // usable by the JIT.
-   llvm::InitializeNativeTarget();
-
-   llvm::InitializeNativeTargetAsmPrinter();
-
-   llvm::InitializeNativeTargetDisassembler();
+   gallivm_init_llvm_begin();
+   gallivm_init_llvm_end();
 }
 
 
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_misc.h b/src/gallium/auxiliary/gallivm/lp_bld_misc.h
index 36923aa..f87bb24 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_misc.h
+++ b/src/gallium/auxiliary/gallivm/lp_bld_misc.h
@@ -41,6 +41,11 @@ extern "C" {
 
 struct lp_generated_code;
 
+extern void
+gallivm_init_llvm_begin(void);
+
+extern void
+gallivm_init_llvm_end(void);
 
 extern void
 lp_set_target_options(void);
-- 
2.0.4