[kernel-hardening] Re: Conversion from atomic_t to refcount_t: summary of issues

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Dec 01, 2016 at 04:31:16PM -0500, David Windsor wrote:
> Also, I'd like to point out that while identifying stats_t instances, I
> have found a similar distribution of non-standard functions (as agreed upon
> for the stats_t API).

> First, usage of atomic_long_wrap_t (there currently isn't a stats_long_t
> planned for implementation):

There isn't even a stats_t planned. I'm still very much not convinced
stats_t is needed or even makes sense.

It wouldn't have any different semantics from atomic_t, and the only
argument Kees made was that reduced atomic_t usage would make it easier
to spot refcounts, but you're already building tools to find those.

Once the tools work, who cares.

> Next, API calls outside of the proposed stats_t API:
> 
> kernel/auditsc.c:2029:
>    if (uid_valid(loginuid))
>         sessionid = (unsigned int)atomic_inc_return_wrap(&session_id);

This is _NOT_ a statistic counter and should not be stats_t

> kernel/padata.c:58:
>     seq_nr = atomic_inc_return_wrap(&pd->seq_nr);

Idem

> kernel/rcu/tree_trace.c:192:
>     s0 += atomic_long_read_wrap(&rdp->exp_workdone0);

Don't get the point, this one is actually trivial.

> kernel/trace/trace_mmiotrace.c:123
>     atomic_xchg_wrap(&dropped_count, 0);
> 
> ... and several others.  Note, these are only from stats_t conversions in
> the kernel/ directory.

And while that thing counts, its not actually a statistics thing.