[Python-3000-checkins] r66186 - in python/branches/py3k: Include/ceval.h Misc/NEWS Python/ceval.c

[antoine.pitrou]

Author: antoine.pitrou
Date: Wed Sep 3 20:34:34 2008
New Revision: 66186

Log:
Issue #3697: "Fatal Python error: Cannot recover from stack overflow"
could be easily encountered under Windows in debug mode when exercising
the recursion limit checking code, due to bogus handling of recursion
limit when USE_STACKCHEK was enabled.

Reviewed by Amaury Forgeot d'Arc on IRC.



Modified:
python/branches/py3k/Include/ceval.h
python/branches/py3k/Misc/NEWS
python/branches/py3k/Python/ceval.c

Modified: python/branches/py3k/Include/ceval.h
==============================================================================
--- python/branches/py3k/Include/ceval.h (original)
+++ python/branches/py3k/Include/ceval.h Wed Sep 3 20:34:34 2008
@@ -42,26 +42,62 @@
PyAPI_FUNC(int) Py_AddPendingCall(int (*func)(void *), void *arg);
PyAPI_FUNC(int) Py_MakePendingCalls(void);

-/* Protection against deeply nested recursive calls */
+/* Protection against deeply nested recursive calls
+
+ In Python 3.0, this protection has two levels:
+ * normal anti-recursion protection is triggered when the recursion level
+ exceeds the current recursion limit. It raises a RuntimeError, and sets
+ the "overflowed" flag in the thread state structure. This flag
+ temporarily *disables* the normal protection; this allows cleanup code
+ to potentially outgrow the recursion limit while processing the
+ RuntimeError.
+ * "last chance" anti-recursion protection is triggered when the recursion
+ level exceeds "current recursion limit + 50". By construction, this
+ protection can only be triggered when the "overflowed" flag is set. It
+ means the cleanup code has itself gone into an infinite loop, or the
+ RuntimeError has been mistakingly ignored. When this protection is
+ triggered, the interpreter aborts with a Fatal Error.
+
+ In addition, the "overflowed" flag is automatically reset when the
+ recursion level drops below "current recursion limit - 50". This heuristic
+ is meant to ensure that the normal anti-recursion protection doesn't get
+ disabled too long.
+
+ Please note: this scheme has its own limitations. See:
+ http://mail.python.org/pipermail/python-dev/2008-August/082106.html
+ for some observations.
+*/
PyAPI_FUNC(void) Py_SetRecursionLimit(int);
PyAPI_FUNC(int) Py_GetRecursionLimit(void);

-#define Py_EnterRecursiveCall(where) \
+#define Py_EnterRecursiveCall(where) \
(_Py_MakeRecCheck(PyThreadState_GET()->recursion_depth) && \
_Py_CheckRecursiveCall(where))
#define Py_LeaveRecursiveCall() \
- do{ if((--PyThreadState_GET()->recursion_depth) < \
- _Py_CheckRecursionLimit - 50) \
- PyThreadState_GET()->overflowed = 0; \
- } while(0)
+ do{ if(_Py_MakeEndRecCheck(PyThreadState_GET()->recursion_depth)) \
+ PyThreadState_GET()->overflowed = 0; \
+ } while(0)
PyAPI_FUNC(int) _Py_CheckRecursiveCall(char *where);
PyAPI_DATA(int) _Py_CheckRecursionLimit;
+
#ifdef USE_STACKCHECK
-# define _Py_MakeRecCheck(x) (++(x) > --_Py_CheckRecursionLimit)
+/* With USE_STACKCHECK, we artificially decrement the recursion limit in order
+ to trigger regular stack checks in _Py_CheckRecursiveCall(), except if
+ the "overflowed" flag is set, in which case we need the true value
+ of _Py_CheckRecursionLimit for _Py_MakeEndRecCheck() to function properly.
+*/
+# define _Py_MakeRecCheck(x) \
+ (++(x) > (_Py_CheckRecursionLimit += PyThreadState_GET()->overflowed - 1))
#else
# define _Py_MakeRecCheck(x) (++(x) > _Py_CheckRecursionLimit)
#endif

+#ifdef USE_STACKCHECK
+# define _Py_MakeEndRecCheck(x) (--(x) < _Py_CheckRecursionLimit - 50)
+#else
+# define _Py_MakeEndRecCheck(x) (--(x) < _Py_CheckRecursionLimit - 50)
+#endif
+
#define Py_ALLOW_RECURSION \
do { unsigned char _old = PyThreadState_GET()->recursion_critical;\
PyThreadState_GET()->recursion_critical = 1;

Modified: python/branches/py3k/Misc/NEWS
==============================================================================
--- python/branches/py3k/Misc/NEWS (original)
+++ python/branches/py3k/Misc/NEWS Wed Sep 3 20:34:34 2008
@@ -12,6 +12,11 @@
Core and Builtins
-----------------

+- Issue #3697: "Fatal Python error: Cannot recover from stack overflow"
+ could be easily encountered under Windows in debug mode when exercising
+ the recursion limit checking code, due to bogus handling of recursion
+ limit when USE_STACKCHEK was enabled.
+
- Issue 3639: The _warnings module could segfault the interpreter when
unexpected types were passed in as arguments.


Modified: python/branches/py3k/Python/ceval.c
==============================================================================
--- python/branches/py3k/Python/ceval.c (original)
+++ python/branches/py3k/Python/ceval.c Wed Sep 3 20:34:34 2008
@@ -471,6 +471,7 @@
return -1;
}
#endif
+ _Py_CheckRecursionLimit = recursion_limit;
if (tstate->recursion_critical)
/* Somebody asked that we don't check for recursion. */
return 0;
@@ -489,7 +490,6 @@
where);
return -1;
}
- _Py_CheckRecursionLimit = recursion_limit;
return 0;
}