Re: [Qemu-devel] [PATCH 11/39] msix: split msix_free from msix_uninit

[Paolo Bonzini <pbonzini@redhat.com>]

Il 05/06/2013 06:32, Michael S. Tsirkin ha scritto:
> On Wed, Jun 05, 2013 at 09:48:19AM +0200, Paolo Bonzini wrote:
>> Il 05/06/2013 06:53, Michael S. Tsirkin ha scritto:
>>> On Wed, Jun 05, 2013 at 12:40:00AM +0200, Paolo Bonzini wrote:
>>>> Il 05/06/2013 00:03, Michael S. Tsirkin ha scritto:
>>>>>>> +    if (dev->msix_table || dev->msix_pba || dev->msix_entry_used) {
>>>>>>> +        msix_free(dev);
>>>>>>> +    }
>>>>>>> +
>>>>>>>      dev->msix_table = g_malloc0(table_size);
>>>>>>>      dev->msix_pba = g_malloc0(pba_size);
>>>>>>>      dev->msix_entry_used = g_malloc0(nentries * sizeof *dev->msix_entry_used);
>>>>> Wow msix_init calls msix_free, and not on error path?
>>>>> What's going on here?
>>>>
>>>> I wasn't too sure that you could get here only with NULL
>>>> msix_table/pba/entry_used and wanted to protect against leaks.  I'll
>>>> change it to an assertion.
>>>
>>> I don't think we should require users allocate all memory with g_malloc0.
>>> So no assertion either.
>>
>> Assertion that is is NULL, followed by g_malloc0?
> 
> No because who sets it to NULL the first time?
> msix_init just started.

When an object is created, it is all-zeroed.

>>> If there's a leak there was always a leak
>>
>> No, there wasn't because msix_uninit would have freed the memory.  That is,
>>
>>     msix_init
>>     msix_uninit
>>     msix_init
>>     msix_uninit
>>
>> had no leak.  Instead, now msix_free is going to be called just once,
>> right before freeing the object itself:
>>
>>     msix_init
>>     msix_uninit
>>     msix_init     ***
>>     msix_uninit
>>     msix_free
>>
>> and will have a leak at ***.
> 
> Yes. And this looks completely sane from outside,
> so this is a bad API.
> The way to fix it is not with asserts in code, we need a good API:
> alloc/free init/uninit ...

Can't, because table_size/pba_size is not available at init time (e.g.
for VFIO not until the host BARs are processed).  What about using
g_realloc + memset?

Paolo