stdlib: More helpful message for the filelock error

Change-Id: Ib8e3bc9fc145a9604670e8288209ac62bfbd7932
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66091
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/gem5/utils/filelock.py

@@ -69,12 +69,22 @@ class FileLock(object):
             except OSError as e:
                 if e.errno != errno.EEXIST:
                     raise
+                solution_message = (
+                    "This is likely due to the existence"
+                    " of the lock file '{}'. If there's no other process"
+                    " the lock file, you can manually delete the lock file and"
+                    " rerun the script.".format(self.lockfile)
+                )
                 if self.timeout is None:
                     raise FileLockException(
-                        "Could not acquire lock on {}".format(self.file_name)
+                        "Could not acquire lock on {}. {}".format(
+                            self.file_name, solution_message
+                        )
                     )
                 if (time.time() - start_time) >= self.timeout:
-                    raise FileLockException("Timeout occured.")
+                    raise FileLockException(
+                        "Timeout occured. {}".format(solution_message)
+                    )
                 time.sleep(self.delay)
 
     #        self.is_locked = True