Fix memory leak for size-zero ndarray (apache#14365)

* free memory for size zero storage handle

* skip adding nullptr into GPU memory pool

* set context for aux handle

* set context for aux handle once it is created

include/mxnet/ndarray.h

@@ -909,9 +909,6 @@ class NDArray {
       // aux_handles always reflect the correct number of aux data
       for (size_t i = 0; i < aux_shapes.size(); i++) {
         CheckAndAllocAuxData(i, aux_shapes[i]);
-        // this line is needed in case when aux_shapes[i].Size() = 0
-        // aux_handles[i] will not be updated and take only default value.
-        aux_handles[i].ctx = ctx;
       }
       if (!delay_alloc) {
         CheckAndAllocData(storage_shape, dtype);
@@ -986,8 +983,8 @@ class NDArray {
 #endif
         delay_alloc = false;
       } else if (shandle.size < dbytes) {
-        // free storage if necessary and alloc again
-        if (shandle.size > 0) Storage::Get()->Free(shandle);
+        // free storage
+        Storage::Get()->Free(shandle);
         // init storage
         shandle = Storage::Get()->Alloc(dbytes, shandle.ctx);
 #if MXNET_USE_MKLDNN == 1
@@ -1052,12 +1049,14 @@ class NDArray {
         << "storage type cannot be kDefaultStorage in CheckAndAllocAuxData";
       if (aux_handles.size() <= i) {
         aux_handles.resize(i + 1);
+        // set context for the newly created aux handle
+        aux_handles[i].ctx = ctx;
       }
       size_t aux_bytes = shape.Size() * mshadow::mshadow_sizeof(aux_types[i]);
       if (aux_handles[i].size < aux_bytes) {
-        // free storage if necessary and alloc again
-        if (aux_handles[i].size > 0) Storage::Get()->Free(aux_handles[i]);
-        // init aux storage
+        // free storage
+        Storage::Get()->Free(aux_handles[i]);
+        // init storage
         aux_handles[i] = Storage::Get()->Alloc(aux_bytes, ctx);
       }
       // init shape

src/ndarray/ndarray.cc

@@ -121,9 +121,9 @@ NDArray::Chunk::~Chunk() {
         CHECK_EQ(mem.mem->GetDataHandle(), mem.h.dptr);
       }
 #endif
-      if (mem.h.size > 0) Storage::Get()->Free(mem.h);
+      Storage::Get()->Free(mem.h);
       for (const auto& aux : mem.aux_h) {
-        if (aux.size > 0) Storage::Get()->Free(aux);
+        Storage::Get()->Free(aux);
       }
     }
   }, shandle.ctx, var);
@@ -134,8 +134,8 @@ void NDArray::Chunk::CheckAndAllocData(const mxnet::TShape &shape, int dtype) {
       << "data is expected to be allocated after aux_data";
   auto dbytes = shape.Size() * mshadow::mshadow_sizeof(dtype);
   if (shandle.size < dbytes) {
-    // free storage if necessary and alloc again
-    if (shandle.size > 0) Storage::Get()->Free(shandle);
+    // free storage
+    Storage::Get()->Free(shandle);
     // init storage
     shandle = Storage::Get()->Alloc(dbytes, ctx);
 #if MXNET_USE_MKLDNN == 1

src/storage/pooled_storage_manager.h

@@ -155,6 +155,10 @@ void GPUPooledStorageManager::Alloc(Storage::Handle* handle) {
 }
 
 void GPUPooledStorageManager::Free(Storage::Handle handle) {
+  // Do nothing if dptr is nullptr. Otherwise, nullptr may be reused
+  // which can cause illegal memory access error.
+  if (handle.dptr == nullptr) return;
+
   std::lock_guard<std::mutex> lock(Storage::Get()->GetMutex(Context::kGPU));
   size_t size = RoundAllocSize(handle.size);
   auto&& reuse_pool = memory_pool_[size];
@@ -312,6 +316,10 @@ void GPUPooledRoundedStorageManager::Alloc(Storage::Handle* handle) {
 }
 
 void GPUPooledRoundedStorageManager::Free(Storage::Handle handle) {
+  // Do nothing if dptr is nullptr. Otherwise, nullptr may be reused
+  // which can cause illegal memory access error.
+  if (handle.dptr == nullptr) return;
+
   std::lock_guard<std::mutex> lock(Storage::Get()->GetMutex(Context::kGPU));
   int bucket = get_bucket(handle.size);
   auto&& reuse_pool = memory_pool_[bucket];