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Message-ID: <20161201230328.GS3045@worktop.programming.kicks-ass.net>
Date: Fri, 2 Dec 2016 00:03:28 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: David Windsor <dwindsor@...il.com>
Cc: "Reshetova, Elena" <elena.reshetova@...el.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Greg KH <gregkh@...uxfoundation.org>,
Kees Cook <keescook@...omium.org>,
"will.deacon@....com" <will.deacon@....com>,
Boqun Feng <boqun.feng@...il.com>,
Hans Liljestrand <ishkamiel@...il.com>,
"aik@...abs.ru" <aik@...abs.ru>,
"david@...son.dropbear.id.au" <david@...son.dropbear.id.au>
Subject: Re: Conversion from atomic_t to refcount_t: summary of issues
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.
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