Re: [PATCH] tests/qtest: Plug memory leaks in qtest_get_machines

[Thomas Huth <thuth@redhat.com>]

On 23/01/2023 22.22, Fabiano Rosas wrote:
> Thomas Huth <thuth@redhat.com> writes:
> 
>> On 23/01/2023 14.32, Fabiano Rosas wrote:
>>> Thomas Huth <thuth@redhat.com> writes:
>>>
>>>> On 20/01/2023 20.44, Fabiano Rosas wrote:
>>>>> These leaks can be avoided:
>>>>>
>>>>>     759 bytes in 61 blocks are still reachable in loss record 56 of 60
>>>>>        at 0x4034744: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
>>>>>        by 0x4A88518: g_malloc (in /usr/lib64/libglib-2.0.so.0.7000.5)
>>>>>        by 0x4AA313E: g_strdup (in /usr/lib64/libglib-2.0.so.0.7000.5)
>>>>>        by 0x12083E: qtest_get_machines (libqtest.c:1323)
>>>>>        by 0x12098C: qtest_cb_for_every_machine (libqtest.c:1348)
>>>>>        by 0x11556C: main (test-hmp.c:160)
>>>>>
>>>>>     992 bytes in 1 blocks are still reachable in loss record 57 of 60
>>>>>        at 0x4034744: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
>>>>>        by 0x4A88518: g_malloc (in /usr/lib64/libglib-2.0.so.0.7000.5)
>>>>>        by 0x120725: qtest_get_machines (libqtest.c:1313)
>>>>>        by 0x12098C: qtest_cb_for_every_machine (libqtest.c:1348)
>>>>>        by 0x11556C: main (test-hmp.c:160)
...
>> (Also, it's valgrind that you used, isn't it? - I wonder why it's
>> complaining here at all since the pointer to the memory should still be
>> valid at the end?)
> 
> valgrind is complaining about the memory not being explicitly freed at
> any point. I guess "leak" was not the most precise term to use in the
> commit message.

How did you run valgrind? For me, it does not really complain about the 
non-freed memory here since it is still reachable. The only difference that 
I see is in the summary. Without your patch:

     still reachable: 27,471 bytes in 152 blocks

with your patch:

     still reachable: 25,713 bytes in 88 blocks

... but that IMHO doesn't really hurt, since the memory is not really 
leaked, i.e. the memory usage won't increase during runtime here. So I fail 
to see which problem you're really trying to solve here, could you please 
elaborate?

  Thomas