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Re: [libvirt] [PATCH] daemon: Plug memory leaks



On Thu, Apr 12, 2012 at 03:24:08PM +0800, Alex Jia wrote:
> Detected by valgrind. Leaks are introduced in commit 6e6e9be.
> 
> * daemon/libvirtd-config.c (macro GET_CONF_STR): fix memory leaks.
> 
> How to reproduce?
> 
> % make && make -C tests check TESTS=libvirtdconftest
> % cd tests && valgrind -v --leak-check=full ./libvirtdconftest
> 
> actual result:
> 
> ==11008== 185 bytes in 5 blocks are definitely lost in loss record 3 of 5
> ==11008==    at 0x4A05FDE: malloc (vg_replace_malloc.c:236)
> ==11008==    by 0x39CF07F6E1: strdup (strdup.c:43)
> ==11008==    by 0x406626: daemonConfigLoadOptions (libvirtd-config.c:438)
> ==11008==    by 0x406800: daemonConfigLoadData (libvirtd-config.c:492)
> ==11008==    by 0x403CCF: testCorrupt (libvirtdconftest.c:110)
> ==11008==    by 0x404FAD: virtTestRun (testutils.c:145)
> ==11008==    by 0x403A34: mymain (libvirtdconftest.c:219)
> ==11008==    by 0x404687: virtTestMain (testutils.c:700)
> ==11008==    by 0x39CF01ECDC: (below main) (libc-start.c:226)
> ==11008==
> ==11008== LEAK SUMMARY:
> ==11008==    definitely lost: 185 bytes in 5 blocks
> 
> Signed-off-by: Alex Jia <ajia redhat com>
> ---
>  daemon/libvirtd-config.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/daemon/libvirtd-config.c b/daemon/libvirtd-config.c
> index 4d041f0..0a4323a 100644
> --- a/daemon/libvirtd-config.c
> +++ b/daemon/libvirtd-config.c
> @@ -152,6 +152,7 @@ checkType (virConfValuePtr p, const char *filename,
>                  virReportOOMError();                                    \
>                  goto error;                                             \
>              }                                                           \
> +            VIR_FREE(data->var_name);                                   \
>          }                                                               \
>      } while (0)

Errr, no. Please look at the context of what's going on, rather than
just blindly adding code to free a block at the point where valgrind
shows the allocation.

The full context to this diff

#define GET_CONF_STR(conf, filename, var_name)                          \
    do {                                                                \
        virConfValuePtr p = virConfGetValue (conf, #var_name);          \
        if (p) {                                                        \
            if (checkType (p, filename, #var_name, VIR_CONF_STRING) < 0) \
                goto error;                                             \
            VIR_FREE(data->var_name);                                   \
            if (!(data->var_name = strdup (p->str))) {                  \
                virReportOOMError();                                    \
                goto error;                                             \
            }                                                           \
        }                                                               \
    } while (0)


Your suggested change means we would be free'ing the config file before
we have even used it.

If you look at this line:

> ==11008==    by 0x406626: daemonConfigLoadOptions (libvirtd-config.c:438)

You'll see it matches:

    GET_CONF_STR (conf, filename, host_uuid);

There are no leak reports for other uses of GET_CONF_STR, so this suggests
that 'host_uuid' is not being freed. Check daemonConfigFree and you'll see
this is indeed missing

Daniel
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