Re: [Qemu-devel] [PULL 00/22] Docker and block patches

[Paolo Bonzini]

On 30/05/2017 11:33, Fam Zheng wrote:
> On Tue, 05/30 10:19, Stefan Hajnoczi wrote:
>> On Fri, May 26, 2017 at 03:52:24PM +0800, Fam Zheng wrote:
>>> The following changes since commit 9964e96dc9999cf7f7c936ee854a795415d19b60:
>>>
>>>   Merge remote-tracking branch 'jasowang/tags/net-pull-request' into 
>>> staging (2017-05-23 15:01:31 +0100)
>>>
>>> are available in the git repository at:
>>>
>>>   git://github.com/famz/qemu.git tags/docker-and-block-pull-request
>>>
>>> for you to fetch changes up to 77269bba94ef97de99ae61fdc98629a8704ae2ed:
>>>
>>>   block: make accounting thread-safe (2017-05-26 09:25:30 +0800)
>>>
>>> ----------------------------------------------------------------
>>>
>>> For Paolo's block layer thread safety part I and my docker testing
>>> enhancements.
>>
>> Please fix the checkpatch issues.
> 
> Paolo, could you provide the comments that can be added to the memory 
> barriers?

It's a false positive.  The comments are just a couple lines above:

        /* We have to set low before high, just like stat64_max reads
         * high before low.  The value may become lower temporarily, but
         * stat64_get does not notice (it takes the lock) and the only ill
         * effect on stat64_max is that the slow path may be triggered
         * unnecessarily.
         */
        atomic_set(&s->low, (uint32_t)value);
        smp_wmb();
        atomic_set(&s->high, value >> 32);

Paolo