Fix overflow error in GPU batched linear algebra kernels.

As reported in jax-ml#24843, our LU decomposition on GPU hits overflow errors when the batch size approaches int32 max. This was caused by an issue in how we were constructing the batched pointers used by cuBLAS.

PiperOrigin-RevId: 695694648

Author: dfm

jaxlib/gpu/make_batch_pointers.cu.cc

@@ -16,6 +16,7 @@ limitations under the License.
 #include "jaxlib/gpu/make_batch_pointers.h"
 
 #include <algorithm>
+#include <cstdint>
 
 #include "jaxlib/gpu/vendor.h"
 
@@ -24,17 +25,19 @@ namespace JAX_GPU_NAMESPACE {
 
 namespace {
 __global__ void MakeBatchPointersAsyncKernel(char* buffer_in, void** buffer_out,
-                                             int batch, int batch_elem_size) {
-  for (int idx = blockIdx.x * blockDim.x + threadIdx.x; idx < batch;
+                                             int64_t batch,
+                                             int64_t batch_elem_size) {
+  for (int64_t idx = blockIdx.x * blockDim.x + threadIdx.x; idx < batch;
        idx += blockDim.x * gridDim.x) {
     buffer_out[idx] = buffer_in + idx * batch_elem_size;
   }
 }
 }  // namespace
 
 void MakeBatchPointersAsync(gpuStream_t stream, void* buffer_in,
-                            void* buffer_out, int batch, int batch_elem_size) {
-  const int block_dim = 128;
+                            void* buffer_out, int64_t batch,
+                            int64_t batch_elem_size) {
+  const std::size_t block_dim = 128;
   const std::size_t grid_dim =
       std::min<std::size_t>(1024, (batch + block_dim - 1) / block_dim);
   MakeBatchPointersAsyncKernel<<<grid_dim, block_dim, 0, stream>>>(

jaxlib/gpu/make_batch_pointers.h

@@ -16,13 +16,16 @@ limitations under the License.
 #ifndef JAXLIB_GPU_MAKE_BATCH_POINTERS_H_
 #define JAXLIB_GPU_MAKE_BATCH_POINTERS_H_
 
+#include <cstdint>
+
 #include "jaxlib/gpu/vendor.h"
 
 namespace jax {
 namespace JAX_GPU_NAMESPACE {
 
 void MakeBatchPointersAsync(gpuStream_t stream, void* buffer_in,
-                            void* buffer_out, int batch, int batch_elem_size);
+                            void* buffer_out, int64_t batch,
+                            int64_t batch_elem_size);
 
 }  // namespace JAX_GPU_NAMESPACE
 }  // namespace jax

tests/linalg_test.py

@@ -1450,6 +1450,14 @@ def testLuBatching(self, shape, dtype):
     self.assertAllClose(ls, actual_ls, rtol=5e-6)
     self.assertAllClose(us, actual_us)
 
+  @jtu.skip_on_devices("cpu", "tpu")
+  @jtu.skip_on_flag("jax_skip_slow_tests", True)
+  def testBatchedLuOverflow(self):
+    # see https://github.com/jax-ml/jax/issues/24843
+    x = self.rng().standard_normal((1500000, 20, 20)).astype(np.float32)
+    lu, _, _ = lax.linalg.lu(x)
+    self.assertTrue(jnp.all(lu.std(axis=[1, 2]) > 0.9))
+
   @jtu.skip_on_devices("cpu", "tpu")
   @jtu.ignore_warning(category=DeprecationWarning,
                       message="backend and device argument")