Remove duplicate no_grad context managers (#16773)

src/lightning/pytorch/loops/epoch/training_epoch_loop.py

@@ -15,8 +15,6 @@ import math
 from collections import OrderedDict
 from typing import Any, Dict, Optional, Union
 
-import torch
-
 import lightning.pytorch as pl
 from lightning.pytorch import loops  # import as loops to avoid circular imports
 from lightning.pytorch.loops.fetchers import _DataFetcher, _DataLoaderIterDataFetcher
@@ -284,8 +282,7 @@ class _TrainingEpochLoop(loops._Loop):
         # reload dataloaders
         self.val_loop._reload_evaluation_dataloaders()
 
-        with torch.no_grad():
-            self.val_loop.run()
+        self.val_loop.run()
 
     def _accumulated_batches_reached(self) -> bool:
         """Determine if accumulation will be finished by the end of the current batch."""

src/lightning/pytorch/trainer/trainer.py

@@ -956,8 +956,7 @@ class Trainer:
             ]
 
             # run eval step
-            with torch.no_grad():
-                val_loop.run()
+            val_loop.run()
 
             call._call_callback_hooks(self, "on_sanity_check_end")