Fixed #21134 -- Prevented queries in broken transactions.

Backport of 728548e4 from master.

Squashed commit of the following:

commit 63ddb271a44df389b2c302e421fc17b7f0529755
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Sep 29 22:51:00 2013 +0200

    Clarified interactions between atomic and exceptions.

commit 2899ec299228217c876ba3aa4024e523a41c8504
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Sep 22 22:45:32 2013 +0200

    Fixed TransactionManagementError in tests.

    Previous commit introduced an additional check to prevent running
    queries in transactions that will be rolled back, which triggered a few
    failures in the tests. In practice using transaction.atomic instead of
    the low-level savepoint APIs was enough to fix the problems.

commit 4a639b059ea80aeb78f7f160a7d4b9f609b9c238
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Tue Sep 24 22:24:17 2013 +0200

    Allowed nesting constraint_checks_disabled inside atomic.

    Since MySQL handles transactions loosely, this isn't a problem.

commit 2a4ab1cb6e83391ff7e25d08479e230ca564bfef
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sat Sep 21 18:43:12 2013 +0200

    Prevented running queries in transactions that will be rolled back.

    This avoids a counter-intuitive behavior in an edge case on databases
    with non-atomic transaction semantics.

    It prevents using savepoint_rollback() inside an atomic block without
    calling set_rollback(False) first, which is backwards-incompatible in
    tests.

    Refs #21134.

commit 8e3db393853c7ac64a445b66e57f3620a3fde7b0
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Sep 22 22:14:17 2013 +0200

    Replaced manual savepoints by atomic blocks.

    This ensures the rollback flag is handled consistently in internal APIs.

8 files changed, 60 insertions, 27 deletions

diff --git a/django/contrib/sessions/backends/db.py b/django/contrib/sessions/backends/db.py
index 206fca2700..7be99c3e16 100644
--- a/django/contrib/sessions/backends/db.py
+++ b/django/contrib/sessions/backends/db.py
@@ -58,12 +58,11 @@ class SessionStore(SessionBase):
             expire_date=self.get_expiry_date()
         )
         using = router.db_for_write(Session, instance=obj)
-        sid = transaction.savepoint(using=using)
         try:
-            obj.save(force_insert=must_create, using=using)
+            with transaction.atomic(using=using):
+                obj.save(force_insert=must_create, using=using)
         except IntegrityError:
             if must_create:
-                transaction.savepoint_rollback(sid, using=using)
                 raise CreateError
             raise
 
diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index f06682f630..55ed1f0a16 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -359,6 +359,12 @@ class BaseDatabaseWrapper(object):
             raise TransactionManagementError(
                 "This is forbidden when an 'atomic' block is active.")
 
+    def validate_no_broken_transaction(self):
+        if self.needs_rollback:
+            raise TransactionManagementError(
+                "An error occurred in the current transaction. You can't "
+                "execute queries until the end of the 'atomic' block.")
+
     def abort(self):
         """
         Roll back any ongoing transaction and clean the transaction state
@@ -626,6 +632,9 @@ class BaseDatabaseFeatures(object):
     # when autocommit is disabled? http://bugs.python.org/issue8145#msg109965
     autocommits_when_autocommit_is_off = False
 
+    # Does the backend prevent running SQL queries in broken transactions?
+    atomic_transactions = True
+
     # Does the backend support 'pyformat' style ("... %(name)s ...", {'name': value})
     # parameter passing? Note this can be provided by the backend even if not
     # supported by the Python driver
diff --git a/django/db/backends/mysql/base.py b/django/db/backends/mysql/base.py
index fa64175ffc..d760418aaf 100644
--- a/django/db/backends/mysql/base.py
+++ b/django/db/backends/mysql/base.py
@@ -166,6 +166,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     requires_explicit_null_ordering_when_grouping = True
     allows_primary_key_0 = False
     uses_savepoints = True
+    atomic_transactions = False
 
     def __init__(self, connection):
         super(DatabaseFeatures, self).__init__(connection)
@@ -470,7 +471,13 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         """
         Re-enable foreign key checks after they have been disabled.
         """
-        self.cursor().execute('SET foreign_key_checks=1')
+        # Override needs_rollback in case constraint_checks_disabled is
+        # nested inside transaction.atomic.
+        self.needs_rollback, needs_rollback = False, self.needs_rollback
+        try:
+            self.cursor().execute('SET foreign_key_checks=1')
+        finally:
+            self.needs_rollback = needs_rollback
 
     def check_constraints(self, table_names=None):
         """
diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index 9e7dd03fc2..46f89ffd2f 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -89,6 +89,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     has_bulk_insert = True
     supports_tablespaces = True
     supports_sequence_reset = False
+    atomic_transactions = False
 
 class DatabaseOperations(BaseDatabaseOperations):
     compiler_module = "django.db.backends.oracle.compiler"
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index 2255cc2a8c..89c9ef1afa 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -101,6 +101,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     has_bulk_insert = True
     can_combine_inserts_with_and_without_auto_increment_pk = False
     autocommits_when_autocommit_is_off = True
+    atomic_transactions = False
     supports_paramstyle_pyformat = False
 
     @cached_property
diff --git a/django/db/backends/util.py b/django/db/backends/util.py
index 43ceff095b..2820007b1c 100644
--- a/django/db/backends/util.py
+++ b/django/db/backends/util.py
@@ -19,14 +19,9 @@ class CursorWrapper(object):
         self.cursor = cursor
         self.db = db
 
-    SET_DIRTY_ATTRS = frozenset(['execute', 'executemany', 'callproc'])
-    WRAP_ERROR_ATTRS = frozenset([
-        'callproc', 'close', 'execute', 'executemany',
-        'fetchone', 'fetchmany', 'fetchall', 'nextset'])
+    WRAP_ERROR_ATTRS = frozenset(['fetchone', 'fetchmany', 'fetchall', 'nextset'])
 
     def __getattr__(self, attr):
-        if attr in CursorWrapper.SET_DIRTY_ATTRS:
-            self.db.set_dirty()
         cursor_attr = getattr(self.cursor, attr)
         if attr in CursorWrapper.WRAP_ERROR_ATTRS:
             return self.db.wrap_database_errors(cursor_attr)
@@ -36,18 +31,42 @@ class CursorWrapper(object):
     def __iter__(self):
         return iter(self.cursor)
 
+    # The following methods cannot be implemented in __getattr__, because the
+    # code must run when the method is invoked, not just when it is accessed.
 
-class CursorDebugWrapper(CursorWrapper):
+    def callproc(self, procname, params=None):
+        self.db.validate_no_broken_transaction()
+        self.db.set_dirty()
+        with self.db.wrap_database_errors:
+            if params is None:
+                return self.cursor.callproc(procname)
+            else:
+                return self.cursor.callproc(procname, params)
 
     def execute(self, sql, params=None):
+        self.db.validate_no_broken_transaction()
         self.db.set_dirty()
+        with self.db.wrap_database_errors:
+            if params is None:
+                return self.cursor.execute(sql)
+            else:
+                return self.cursor.execute(sql, params)
+
+    def executemany(self, sql, param_list):
+        self.db.validate_no_broken_transaction()
+        self.db.set_dirty()
+        with self.db.wrap_database_errors:
+            return self.cursor.executemany(sql, param_list)
+
+
+class CursorDebugWrapper(CursorWrapper):
+
+    # XXX callproc isn't instrumented at this time.
+
+    def execute(self, sql, params=None):
         start = time()
         try:
-            with self.db.wrap_database_errors:
-                if params is None:
-                    # params default might be backend specific
-                    return self.cursor.execute(sql)
-                return self.cursor.execute(sql, params)
+            return super(CursorDebugWrapper, self).execute(sql, params)
         finally:
             stop = time()
             duration = stop - start
@@ -61,11 +80,9 @@ class CursorDebugWrapper(CursorWrapper):
             )
 
     def executemany(self, sql, param_list):
-        self.db.set_dirty()
         start = time()
         try:
-            with self.db.wrap_database_errors:
-                return self.cursor.executemany(sql, param_list)
+            return super(CursorDebugWrapper, self).executemany(sql, param_list)
         finally:
             stop = time()
             duration = stop - start
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 31b79ed0a2..1075407ae3 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -376,12 +376,10 @@ class QuerySet(object):
                 params = dict((k, v) for k, v in kwargs.items() if LOOKUP_SEP not in k)
                 params.update(defaults)
                 obj = self.model(**params)
-                sid = transaction.savepoint(using=self.db)
-                obj.save(force_insert=True, using=self.db)
-                transaction.savepoint_commit(sid, using=self.db)
+                with transaction.atomic(using=self.db):
+                    obj.save(force_insert=True, using=self.db)
                 return obj, True
             except DatabaseError:
-                transaction.savepoint_rollback(sid, using=self.db)
                 exc_info = sys.exc_info()
                 try:
                     return self.get(**lookup), False
diff --git a/django/db/transaction.py b/django/db/transaction.py
index 15da007ec9..2639569122 100644
--- a/django/db/transaction.py
+++ b/django/db/transaction.py
@@ -16,14 +16,15 @@ import warnings
 
 from functools import wraps
 
-from django.db import connections, DatabaseError, DEFAULT_DB_ALIAS
+from django.db import (
+        connections, DEFAULT_DB_ALIAS,
+        DatabaseError, ProgrammingError)
 from django.utils.decorators import available_attrs
 
 
-class TransactionManagementError(Exception):
+class TransactionManagementError(ProgrammingError):
     """
-    This exception is thrown when something bad happens with transaction
-    management.
+    This exception is thrown when transaction management is used improperly.
     """
     pass