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Re: [libvirt] [PATCH] remote: avoid memory leak on successful path



On 01/18/2012 05:32 AM, Eric Blake wrote:
On 01/17/2012 02:59 AM, ajia redhat com wrote:
From: Alex Jia<ajia redhat com>

when everything is okay, 'rv' will be 0, however, 'cleanup' lable only free
allocated memory with 'rv<  0', so memory leak on successful path. The patch
uses new virTypedParameterArrayClear function to free memory instead.

* src/remote/remote_driver.c: fix memory leak on remoteDeserializeTypedParameters.

* Detected by valgrind:

==31957== 1 bytes in 1 blocks are definitely lost in loss record 1 of 2,097
==31957==    at 0x4A05FDE: malloc (vg_replace_malloc.c:236)
==31957==    by 0x39CF07F6E1: strdup (in /lib64/libc-2.12.so)
==31957==    by 0xD84CDA1: remoteDeserializeTypedParameters.clone.0 (remote_driver.c:1404)
==31957==    by 0xD84D11B: remoteDomainGetNumaParameters (remote_driver.c:1566)
==31957==    by 0xD81EBFA: virDomainGetNumaParameters (libvirt.c:3887)
==31957==    by 0xD4F8E25: libvirt_virDomainGetNumaParameters (libvirt-override.c:1127)
==31957==    by 0x39E1ADE7F3: PyEval_EvalFrameEx (ceval.c:3794)
==31957==    by 0x39E1ADF99E: PyEval_EvalFrameEx (ceval.c:3880)
==31957==    by 0x39E1AE0466: PyEval_EvalCodeEx (ceval.c:3044)
==31957==    by 0x39E1AE0541: PyEval_EvalCode (ceval.c:545)
==31957==    by 0x39E1AFB88B: run_mod (pythonrun.c:1351)
==31957==    by 0x39E1AFB95F: PyRun_FileExFlags (pythonrun.c:1337)


Signed-off-by: Alex Jia<ajia redhat com>
---
  src/remote/remote_driver.c |    7 +------
  1 files changed, 1 insertions(+), 6 deletions(-)
NACK.  Since params is an incoming parameter, it is up to the caller to
free params, including its contents, on success.

The memory leak resides instead in libvirt_virDomainGetNumaParameters,
and you already posted a patch for a similar leak once:

https://www.redhat.com/archives/libvir-list/2011-December/msg01132.html
Yeah, I have ever done a similar fixing :(
However, my problem with the patch at that time is that we have a LOT of
coding bugs in libvirt-override.c (we are disregarding allocation
failures, failing to propagate python errors back to the caller, and so
forth), where we are better off doing an audit of that entire file:

https://www.redhat.com/archives/libvir-list/2011-December/msg01146.html

In addition, in python/typewrappers.c, we have 2 wrapper functions
'libvirt_constcharPtrWrap' and 'libvirt_constcharPtrWrap', which are
calling 'PyString_FromString' to return new reference of a string, but
they haven't released original string memory, I tried to free them using
free((void *) str), however, it seems it's a wrong, I met some invalid
read/free error in valgrind, the leaks still exist, If we can't free them in
python/typewrappers.c, it means caller must to free them in
libvirt-override.c.

Moreover, I saw we increased object reference in wrapper functions
from python/typewrappers.c by calling 'Py_INCREF', I'm not sure whether
we also need a 'Py_DECREF' in libvirt-override.c when calling wrapper
functions?
+++ b/src/remote/remote_driver.c
@@ -1417,12 +1417,7 @@ remoteDeserializeTypedParameters(remote_typed_param *ret_params_val,
      rv = 0;

  cleanup:
-    if (rv<  0) {
-        int j;
-        for (j = 0; j<  i; j++)
-            if (params[j].type == VIR_TYPED_PARAM_STRING)
-                VIR_FREE(params[j].value.s);
-    }
+    virTypedParameterArrayClear(params, *nparams);
If you want to touch remote_driver.c, to simplify this block of code,
you could use:

if (rv<  0)
     virTypedParameterArrayClear(params, *nparams);
Yeah, but it will be better if we can commit a patch instead of many small patches
to simplify all of related codes :)
rather than open-coding the cleanup loop.  But that still won't solve
the fact that the real leak that needs to be plugged is in
libvirt-override.c.

In deed.


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