[PATCH] nvmet: protect sqhd update by a lock

[James Smart]

On 10/16/2017 12:21 AM, Johannes Thumshirn wrote:
> To me it looks a bit awkward why you're only protecting the RMW part but not
> the re-read below.
> 
> Could you please give some explanation why this is not needed?
> 
> Thanks,
> 	Johannes
> 

Agree, is a little awkward. But works fine. The re-read will contain at 
least the value that it was updated to under the lock. If it's actually 
the value of a simultaneous update that is one further, that's actually 
fine too - as sqhd isn't 1:1 with a cqe. Yes a cqe must contain the 
sqhd, but sqhd can increment independently from a particuluar cqe. Key 
is that sqhd itself must increment sanely so that whenever stamped in a 
cqe it's valid.

I have no problem recutting with the lock around the assignment if desired.

-- james