Re: [PATCH 3/5] fs, xfs: convert xlog_ticket.t_ref from atomic_t to refcount_t

[Kees Cook]

On Wed, Mar 8, 2017 at 7:50 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>> -     ASSERT(atomic_read(&ticket->t_ref) > 0);
>> -     atomic_inc(&ticket->t_ref);
>> +     ASSERT(refcount_read(&ticket->t_ref) > 0);
>> +     refcount_inc(&ticket->t_ref);
>
> With strict refcount semantics refcount_inc should check that
> the count is larger than 0, otherwise we'd need to use
> recount_inc_not_zero or whatever you're going to call it.
>
> Is that something the recount code does / could do?

Yes, refcount_inc() will not increment from 0 and WARNs. It looks like
xfs's ASSERT is also a warn (though with XFS-specific formatting), so
perhaps the ASSERT could be dropped? IIUC, Elena's approach to these
changes was to be conservative about removing the existing checks.

-Kees

-- 
Kees Cook
Pixel Security