Sanitize profile filename

src/lightning/pytorch/CHANGELOG.md

@@ -20,6 +20,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 -
 
+### Fixed
+
+- Sanitize profiler filenames when saving to avoid crashes due to invalid characters ([#21395](https://github.com/Lightning-AI/pytorch-lightning/pull/21395))
+
 
 ## [2.6.0] - 2025-11-28
 

src/lightning/pytorch/profilers/profiler.py

@@ -15,6 +15,7 @@
 
 import logging
 import os
+import re
 from abc import ABC, abstractmethod
 from collections.abc import Generator
 from contextlib import contextmanager
@@ -81,6 +82,7 @@ def _prepare_filename(
         action_name: Optional[str] = None,
         extension: str = ".txt",
         split_token: str = "-",  # noqa: S107
+        sanitize: bool = True,
     ) -> str:
         args = []
         if self._stage is not None:
@@ -91,7 +93,15 @@ def _prepare_filename(
             args.append(str(self._local_rank))
         if action_name is not None:
             args.append(action_name)
-        return split_token.join(args) + extension
+        base = split_token.join(args)
+        if sanitize:
+            # Replace a set of path-unsafe characters across platforms with '_'
+            base = re.sub(r"[\\/:*?\"<>|\n\r\t]", "_", base)
+            base = re.sub(r"_+", "_", base)
+            base = base.strip()
+            if not base:
+                base = "profile"
+        return base + extension
 
     def _prepare_streams(self) -> None:
         if self._write_stream is not None:

tests/tests_pytorch/profilers/test_profiler.py

@@ -322,6 +322,33 @@ def test_advanced_profiler_dump_states(tmp_path):
     assert len(data) > 0
 
 
+@pytest.mark.parametrize("char", ["/", "\\", ":", "*", "?", '"', "<", ">", "|", "\n", "\r", "\t"])
+def test_advanced_profiler_dump_states_sanitizes_filename(tmp_path, char):
+    """Profiler should sanitize action names to produce filesystem-safe .prof filenames.
+
+    This guards against errors when callbacks or actions include path-unsafe characters (e.g., metric names with '/').
+
+    """
+    profiler = AdvancedProfiler(dirpath=tmp_path, dump_stats=True)
+    action_name = f"before{char}after"
+    with profiler.profile(action_name):
+        pass
+
+    profiler.describe()
+
+    prof_files = [f for f in os.listdir(tmp_path) if f.endswith(".prof")]
+    assert len(prof_files) == 1
+    prof_name = prof_files[0]
+
+    # Ensure none of the path-unsafe characters are present in the produced filename
+    forbidden = ["/", "\\", ":", "*", "?", '"', "<", ">", "|", "\n", "\r", "\t"]
+    for bad in forbidden:
+        assert bad not in prof_name
+
+    # File should be non-empty
+    assert (tmp_path / prof_name).read_bytes()
+
+
 def test_advanced_profiler_value_errors(advanced_profiler):
     """Ensure errors are raised where expected."""
     action = "test"