gh-117755: Remove tests on huge memory allocations (#117938)

Remove unreliable tests on huge memory allocations:

* Remove test_maxcontext_exact_arith() of test_decimal.
  Stefan Krah, test author, agreed on removing the test:
  https://github.com/python/cpython/issues/114331#issuecomment-1925731273
* Remove test_constructor() tests of test_io.
  Sam Gross suggests remove them:
  https://github.com/python/cpython/pull/117809#pullrequestreview-2003889558

On Linux, depending how overcommit is configured, especially on Linux
s390x, a huge memory allocation (half or more of the full address
space) can succeed, but then the process will eat the full system
swap and make the system slower and slower until the whole system
becomes unusable.

Moreover, these tests had to be skipped when Python is built with
sanitizers.

diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index 05dcb25a7e5950437396aaf326cb7be6fa5858f2..7010c34792e093709b6aac094e548f913dac87c3 100644 (file)
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -34,12 +34,10 @@ import numbers
 import locale
 from test.support import (is_resource_enabled,
                           requires_IEEE_754, requires_docstrings,
-                          check_sanitizer,
                           check_disallow_instantiation)
 from test.support import (TestFailed,
                           run_with_locale, cpython_only,
-                          darwin_malloc_err_warning, is_emscripten,
-                          skip_on_s390x)
+                          darwin_malloc_err_warning)
 from test.support.import_helper import import_fresh_module
 from test.support import threading_helper
 from test.support import warnings_helper
@@ -5644,50 +5642,6 @@ class CWhitebox(unittest.TestCase):
             self.assertEqual(Decimal.from_float(cls(101.1)),
                              Decimal.from_float(101.1))
 
-    # Issue 41540:
-    @unittest.skipIf(sys.platform.startswith("aix"),
-                     "AIX: default ulimit: test is flaky because of extreme over-allocation")
-    @unittest.skipIf(is_emscripten, "Test is unstable on Emscripten")
-    @unittest.skipIf(check_sanitizer(address=True, memory=True),
-                     "ASAN/MSAN sanitizer defaults to crashing "
-                     "instead of returning NULL for malloc failure.")
-    # gh-114331: The test allocates 784 271 641 GiB and mimalloc does not fail
-    # to allocate it when using mimalloc on s390x.
-    @skip_on_s390x
-    def test_maxcontext_exact_arith(self):
-
-        # Make sure that exact operations do not raise MemoryError due
-        # to huge intermediate values when the context precision is very
-        # large.
-
-        # The following functions fill the available precision and are
-        # therefore not suitable for large precisions (by design of the
-        # specification).
-        MaxContextSkip = ['logical_invert', 'next_minus', 'next_plus',
-                          'logical_and', 'logical_or', 'logical_xor',
-                          'next_toward', 'rotate', 'shift']
-
-        Decimal = C.Decimal
-        Context = C.Context
-        localcontext = C.localcontext
-
-        # Here only some functions that are likely candidates for triggering a
-        # MemoryError are tested.  deccheck.py has an exhaustive test.
-        maxcontext = Context(prec=C.MAX_PREC, Emin=C.MIN_EMIN, Emax=C.MAX_EMAX)
-        with localcontext(maxcontext):
-            self.assertEqual(Decimal(0).exp(), 1)
-            self.assertEqual(Decimal(1).ln(), 0)
-            self.assertEqual(Decimal(1).log10(), 0)
-            self.assertEqual(Decimal(10**2).log10(), 2)
-            self.assertEqual(Decimal(10**223).log10(), 223)
-            self.assertEqual(Decimal(10**19).logb(), 19)
-            self.assertEqual(Decimal(4).sqrt(), 2)
-            self.assertEqual(Decimal("40E9").sqrt(), Decimal('2.0E+5'))
-            self.assertEqual(divmod(Decimal(10), 3), (3, 1))
-            self.assertEqual(Decimal(10) // 3, 3)
-            self.assertEqual(Decimal(4) / 2, 2)
-            self.assertEqual(Decimal(400) ** -1, Decimal('0.0025'))
-
     def test_c_immutable_types(self):
         SignalDict = type(C.Context().flags)
         SignalDictMixin = SignalDict.__bases__[0]

diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index c3dc0572c58c27e769198ee9160871ff11e17ad4..e5cb08c2cdd04c7ad23e866c3616716368c2c008 100644 (file)
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -40,8 +40,7 @@ from test import support
 from test.support.script_helper import (
     assert_python_ok, assert_python_failure, run_python_until_end)
 from test.support import (
-    import_helper, is_apple, os_helper, skip_if_sanitizer, threading_helper, warnings_helper,
-    skip_on_s390x
+    import_helper, is_apple, os_helper, threading_helper, warnings_helper,
 )
 from test.support.os_helper import FakePath
 
@@ -1698,22 +1697,6 @@ class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
 class CBufferedReaderTest(BufferedReaderTest, SizeofTest):
     tp = io.BufferedReader
 
-    @skip_if_sanitizer(memory=True, address=True, thread=True,
-                       reason="sanitizer defaults to crashing "
-                       "instead of returning NULL for malloc failure.")
-    # gh-117755: The test allocates 9 223 372 036 854 775 807 bytes
-    # (0x7fffffffffffffff) and mimalloc fails with a division by zero on s390x.
-    @skip_on_s390x
-    def test_constructor(self):
-        BufferedReaderTest.test_constructor(self)
-        # The allocation can succeed on 32-bit builds, e.g. with more
-        # than 2 GiB RAM and a 64-bit kernel.
-        if sys.maxsize > 0x7FFFFFFF:
-            rawio = self.MockRawIO()
-            bufio = self.tp(rawio)
-            self.assertRaises((OverflowError, MemoryError, ValueError),
-                bufio.__init__, rawio, sys.maxsize)
-
     def test_initialization(self):
         rawio = self.MockRawIO([b"abc"])
         bufio = self.tp(rawio)
@@ -2069,22 +2052,6 @@ class BufferedWriterTest(unittest.TestCase, CommonBufferedTests):
 class CBufferedWriterTest(BufferedWriterTest, SizeofTest):
     tp = io.BufferedWriter
 
-    @skip_if_sanitizer(memory=True, address=True, thread=True,
-                       reason="sanitizer defaults to crashing "
-                       "instead of returning NULL for malloc failure.")
-    # gh-117755: The test allocates 9 223 372 036 854 775 807 bytes
-    # (0x7fffffffffffffff) and mimalloc fails with a division by zero on s390x.
-    @skip_on_s390x
-    def test_constructor(self):
-        BufferedWriterTest.test_constructor(self)
-        # The allocation can succeed on 32-bit builds, e.g. with more
-        # than 2 GiB RAM and a 64-bit kernel.
-        if sys.maxsize > 0x7FFFFFFF:
-            rawio = self.MockRawIO()
-            bufio = self.tp(rawio)
-            self.assertRaises((OverflowError, MemoryError, ValueError),
-                bufio.__init__, rawio, sys.maxsize)
-
     def test_initialization(self):
         rawio = self.MockRawIO()
         bufio = self.tp(rawio)
@@ -2594,22 +2561,6 @@ class BufferedRandomTest(BufferedReaderTest, BufferedWriterTest):
 class CBufferedRandomTest(BufferedRandomTest, SizeofTest):
     tp = io.BufferedRandom
 
-    @skip_if_sanitizer(memory=True, address=True, thread=True,
-                       reason="sanitizer defaults to crashing "
-                       "instead of returning NULL for malloc failure.")
-    # gh-117755: The test allocates 9 223 372 036 854 775 807 bytes
-    # (0x7fffffffffffffff) and mimalloc fails with a division by zero on s390x.
-    @skip_on_s390x
-    def test_constructor(self):
-        BufferedRandomTest.test_constructor(self)
-        # The allocation can succeed on 32-bit builds, e.g. with more
-        # than 2 GiB RAM and a 64-bit kernel.
-        if sys.maxsize > 0x7FFFFFFF:
-            rawio = self.MockRawIO()
-            bufio = self.tp(rawio)
-            self.assertRaises((OverflowError, MemoryError, ValueError),
-                bufio.__init__, rawio, sys.maxsize)
-
     def test_garbage_collection(self):
         CBufferedReaderTest.test_garbage_collection(self)
         CBufferedWriterTest.test_garbage_collection(self)