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Re: [libvirt] [PATCH] python: Avoid memory leaks on libvirt_virNodeGetMemoryStats

On 02/14/2012 02:11 PM, Eric Blake wrote:
On 02/14/2012 03:08 AM, Peter Krempa wrote:
On 02/14/2012 09:31 AM, ajia redhat com wrote:
From: Alex Jia<ajia redhat com>

Detected by valgrind. Leaks are introduced in commit 17c7795.

* python/libvirt-override.c (libvirt_virNodeGetMemoryStats): fix
memory leaks
and improve codes return value.

For details, please see the following link:
RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=770944

Signed-off-by: Alex Jia<ajia redhat com>
   python/libvirt-override.c |   41
   1 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/python/libvirt-override.c b/python/libvirt-override.c
index 4e8a97e..ecb11ea 100644
--- a/python/libvirt-override.c
+++ b/python/libvirt-override.c
@@ -2426,7 +2426,9 @@ libvirt_virNodeGetCPUStats(PyObject *self
   static PyObject *
   libvirt_virNodeGetMemoryStats(PyObject *self ATTRIBUTE_UNUSED,
PyObject *args)
-    PyObject *ret;
+    PyObject *info, *ret;

I'd initialize ret to VIR_PY_NONE here instead of doing it multiple
times later on.

I'd actually initialize to NULL, not VIR_PY_NONE.  Use of VIR_PY_NONE
increments the reference count on the Python None object; and if you
then later return anything else, you would also have to reduce that
reference count to avoid a resource leak in the form of an un-freeable
python object.

Yes I realized that later on :( (after some reading on creation of python bindings :/)

This label gets called only on a error path, so I'd call it "error"
instead of cleanup.

+    VIR_FREE(stats);
+    Py_XDECREF(key);
+    Py_XDECREF(val);
+    return NULL;

You're returning NULL instead of VIR_PY_NONE. (or the variable err)

And I think that's actually correct!  Returning VIR_PY_NONE is a _valid_
python object, and library code interprets it as "I successfully called
your function, but had no object to return; now you can check for the
libvirt error class to see why, but there is no python exception".
Returning NULL means "I encountered a python exception; you can now
catch that exception".  They are handled quite differently in the
calling code.  Returning VIR_PY_NONE should be reserved for the case
where we called a libvirt API that failed (then libvirt did indeed
populate a libvirt error, and there is no python exception); while
returning NULL should be reserved for the case where a python glue code
failed (such as inability to create a new python dictionary) or where we
explicitly raised a python exception (such as when we detect an OOM
situation and call PyErr_NoMemory()).

I didn't notice this difference :( My review for V2 has still some issues then.


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