Fix block_structure error handling BOM-577 (#21801)

openedx/core/djangoapps/content/block_structure/models.py

@@ -4,6 +4,7 @@ Models used by the block structure framework.
 
 from __future__ import absolute_import
 
+import errno
 from contextlib import contextmanager
 from datetime import datetime
 from logging import getLogger
@@ -117,7 +118,9 @@ def _storage_error_handling(bs_model, operation, is_read_operation=False):
         yield
     except Exception as error:  # pylint: disable=broad-except
         log.exception(u'BlockStructure: Exception %s on store %s; %s.', error.__class__, operation, bs_model)
-        if is_read_operation and isinstance(error, (IOError, SuspiciousOperation)):
+        if isinstance(error, OSError) and error.errno in (errno.EACCES, errno.EPERM):  # pylint: disable=no-member
+            raise
+        elif is_read_operation and isinstance(error, (IOError, SuspiciousOperation)):
             # May have been caused by one of the possible error
             # situations listed above.  Raise BlockStructureNotFound
             # so the block structure can be regenerated and restored.

openedx/core/djangoapps/content/block_structure/tests/test_models.py

@@ -4,6 +4,7 @@ Unit tests for Block Structure models.
 # pylint: disable=protected-access
 from __future__ import absolute_import
 
+import errno
 from itertools import product
 from uuid import uuid4
 
@@ -147,19 +148,23 @@ class BlockStructureModelTestCase(TestCase):
             self._assert_file_count_equal(min(num_prior_edits + 1, prune_keep_count))
 
     @ddt.data(
-        (IOError, BlockStructureNotFound, True),
-        (IOError, IOError, False),
-        (SuspiciousOperation, BlockStructureNotFound, True),
-        (SuspiciousOperation, SuspiciousOperation, False),
-        (OSError, OSError, True),
-        (OSError, OSError, False),
+        (IOError, errno.ENOENT, u'No such file or directory', BlockStructureNotFound, True),
+        (IOError, errno.ENOENT, u'No such file or directory', IOError, False),
+        (SuspiciousOperation, None, None, BlockStructureNotFound, True),
+        (SuspiciousOperation, None, None, SuspiciousOperation, False),
+        (OSError, errno.EACCES, u'Permission denied', OSError, True),
+        (OSError, errno.EACCES, u'Permission denied', OSError, False),
     )
     @ddt.unpack
-    def test_error_handling(self, error_raised_in_operation, expected_error_raised, is_read_operation):
+    def test_error_handling(self, error_raised_in_operation, errno_raised, message_raised,
+                            expected_error_raised, is_read_operation):
         bs_model, _ = BlockStructureModel.update_or_create('test data', **self.params)
         with self.assertRaises(expected_error_raised):
             with _storage_error_handling(bs_model, 'operation', is_read_operation):
-                raise error_raised_in_operation
+                if errno_raised is not None:
+                    raise error_raised_in_operation(errno_raised, message_raised)
+                else:
+                    raise error_raised_in_operation
 
     @patch('openedx.core.djangoapps.content.block_structure.models.log')
     def test_old_mongo_keys(self, mock_log):