# HG changeset patch
# User emellor@xxxxxxxxxxxxxxxxxxxxxx
# Node ID a064c5804eae2893bd19597116c31c41f1a25d41
# Parent bb0e5f7f94fd186868b68379aeb81938a1967d25
Fix race between xspy_read_watch and xspy_watch, by placing the watch in the
xshandle's list of watches *before* registering the watch with Xend.
Closes bug #392.
Signed-off-by: Ewan Mellor <ewan@xxxxxxxxxxxxx>
diff -r bb0e5f7f94fd -r a064c5804eae tools/python/xen/lowlevel/xs/xs.c
--- a/tools/python/xen/lowlevel/xs/xs.c Tue Nov 15 15:24:31 2005
+++ b/tools/python/xen/lowlevel/xs/xs.c Tue Nov 15 16:22:04 2005
@@ -16,7 +16,7 @@
*
* Copyright (C) 2005 Mike Wray Hewlett-Packard
* Copyright (C) 2005 Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
- *
+ * Copyright (C) 2005 XenSource Ltd.
*/
#include <Python.h>
@@ -453,25 +453,20 @@
XsHandle *xsh = (XsHandle *)self;
struct xs_handle *xh = xshandle(self);
- PyObject *val = NULL;
int xsval = 0;
if (!xh)
- goto exit;
+ return NULL;
if (!PyArg_ParseTupleAndKeywords(args, kwds, arg_spec, kwd_spec,
&path, &token))
- goto exit;
+ return NULL;
+
+ /* Note that we have to store the watch token in the xs->watches list
+ before registering the watch with xs_watch, otherwise this function
+ races with xs_read_watch.
+ */
+
Py_INCREF(token);
- sprintf(token_str, "%li", (unsigned long)token);
- Py_BEGIN_ALLOW_THREADS
- xsval = xs_watch(xh, path, token_str);
- Py_END_ALLOW_THREADS
- if (!xsval) {
- PyErr_SetFromErrno(PyExc_RuntimeError);
- Py_DECREF(token);
- goto exit;
- }
-
for (i = 0; i < PyList_Size(xsh->watches); i++) {
if (PyList_GetItem(xsh->watches, i) == Py_None) {
PyList_SetItem(xsh->watches, i, token);
@@ -480,10 +475,26 @@
}
if (i == PyList_Size(xsh->watches))
PyList_Append(xsh->watches, token);
+
+ sprintf(token_str, "%li", (unsigned long)token);
+ Py_BEGIN_ALLOW_THREADS
+ xsval = xs_watch(xh, path, token_str);
+ Py_END_ALLOW_THREADS
+ if (!xsval) {
+ for (i = 0; i < PyList_Size(xsh->watches); i++) {
+ if (PyList_GetItem(xsh->watches, i) == token) {
+ Py_INCREF(Py_None);
+ PyList_SetItem(xsh->watches, i, Py_None);
+ break;
+ }
+ }
+
+ PyErr_SetFromErrno(PyExc_RuntimeError);
+ return NULL;
+ }
+
Py_INCREF(Py_None);
- val = Py_None;
- exit:
- return val;
+ return Py_None;
}
#define xspy_read_watch_doc "\n" \
@@ -944,3 +955,11 @@
module = Py_InitModule(PYPKG, xs_methods);
}
+
+
+/*
+ * Local variables:
+ * c-indent-level: 4
+ * c-basic-offset: 4
+ * End:
+ */
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