Re: [Qemu-devel] [PATCH v2 10/18] hw/nvram/fw_cfg: Add reboot_timeout to FWCfgState

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/8/19 12:04 PM, Laszlo Ersek wrote:
> Hi Phil,
> 
> On 03/08/19 02:32, Philippe Mathieu-Daudé wrote:
>> Due to the contract interface of fw_cfg_add_file(), the
>> 'reboot_timeout' data has to be valid for the lifetime of the
>> FwCfg object. For this reason it is copied on the heap with
>> memdup().
>>
>> The object state, 'FWCfgState', is also meant to be valid during the
>> lifetime of the object.
>> Move the 'reboot_timeout' in FWCfgState to achieve the same purpose.
>> Doing so we avoid a memory leak.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>>  hw/nvram/fw_cfg.c         | 4 +++-
>>  include/hw/nvram/fw_cfg.h | 2 ++
>>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> Currently, there is no memory leak. Right now, the leak is theoretical,
> and it would depend on the fw_cfg object being actually destroyed.

Actually my first motivation came while using valgrind, there are a
bunch of warnings related to the fw_cfg device.
This device is not hotpluggable however, and we don't test it in the
device-introspect-test.

> I think armoring the fw_cfg implementation for such lifetime actions is
> valuable. But, that definitely belongs to its own series, in my opinion.
> 
> In the "hw/nvram/fw_cfg.c" file, I count:
> 
> (a) two "specific purpose" g_memdup() calls, namely in
> fw_cfg_bootsplash() and in fw_cfg_reboot();
> 
> (b) one "generic purpose" g_memdup() call, namely in fw_cfg_add_string();
> 
> (c) two "generic purpose" g_malloc() calls, namely in fw_cfg_add_i16(),
> fw_cfg_add_i32(), and fw_cfg_add_i64(). (The one in fw_cfg_modify_i16()
> does not matter here because the previous blob is freed in that function.)
> 
> Your series deals with (a), namely with fw_cfg_reboot() in this patch,
> and with fw_cfg_bootsplash() in the next one.
> 
> Your series deals with neither (b) nor (c). The

I did a PoC of (b) and (c) but it is a more invasive patchset indeed.

> fw_cfg_add_(string|i16|i32|i64) functions are called from a bunch of
> places however, so if we really intend *not* to leak those copies upon
> fw_cfg destruction, then we'll have to track all of them dynamically, in
> a list for example.

I haven't think of using a list.

> (And that necessitates a separate series for this topic even more.)

OK.

> In turn, once we add dynamic tracking, for those blobs that the
> fw_cfg_add_(string|i16|i32|i64) functions allocate internally -- as they
> are advertized to do --, then we might as well use the same tracking
> infrastructure for (a). In other words, it should not be necessary to
> add the specific fields "reboot_timeout" and "boot_splash" to FWCfgState.

OK, I'll drop these patches from this series.

> 
> Thanks,
> Laszlo
> 
>>
>> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
>> index b73a591eff..182d27f59a 100644
>> --- a/hw/nvram/fw_cfg.c
>> +++ b/hw/nvram/fw_cfg.c
>> @@ -250,7 +250,9 @@ static void fw_cfg_reboot(FWCfgState *s)
>>          }
>>      }
>>  
>> -    fw_cfg_add_file(s, "etc/boot-fail-wait", g_memdup(&rt_val, 4), 4);
>> +    s->reboot_timeout = rt_val;
>> +    fw_cfg_add_file(s, "etc/boot-fail-wait",
>> +                    &s->reboot_timeout, sizeof(s->reboot_timeout));
>>  }
>>  
>>  static void fw_cfg_write(FWCfgState *s, uint8_t value)
>> diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
>> index 828ad9dedc..99f6fafcaa 100644
>> --- a/include/hw/nvram/fw_cfg.h
>> +++ b/include/hw/nvram/fw_cfg.h
>> @@ -53,6 +53,8 @@ struct FWCfgState {
>>      dma_addr_t dma_addr;
>>      AddressSpace *dma_as;
>>      MemoryRegion dma_iomem;
>> +
>> +    uint32_t reboot_timeout;
>>  };
>>  
>>  struct FWCfgIoState {
>>
>