Date: Wed, 7 Dec 2016 14:24:57 +0100 From: Peter Zijlstra <peterz@...radead.org> To: David Windsor <dwindsor@...il.com> Cc: Boqun Feng <boqun.feng@...il.com>, Kees Cook <keescook@...omium.org>, "Reshetova, Elena" <elena.reshetova@...el.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Greg KH <gregkh@...uxfoundation.org>, "will.deacon@....com" <will.deacon@....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 Fri, Dec 02, 2016 at 03:25:42PM -0500, David Windsor wrote: > On Thu, Dec 1, 2016 at 8:17 PM, Boqun Feng <boqun.feng@...il.com> wrote: > > So we currently don't have a clear semantics for stats_t, do we? > > We had a discussion about the stats_t API in another thread. We > agreed upon add(), sub(), inc(), dec(), read() and set(). > > > What kind of atomic_t should be replaced with stats_t? > > stats_t is used for those cases in which an atomic variable is > required, but the overflow of this variable isn't of much concern. > Typically, these types of variables are counters of some kind (rx/tx > counts, etc), but not always. Perhaps "stats_t" isn't the best type > name. We actually used "atomic_wrap_t" in previous iterations. And atomic_wrap_t is a horrid trainwreck. Please as to explain the semantics of atomic_wrap_cmpxchg(). How does wrapping apply to something that doesn't do sign bits. > > In the link David pointed out, there are a few cases where a > > stats_t is put on a correctness-related variable. I don't think > > that's a good place to use stats_t. > > > > Yeah, I just grabbed a few examples I noted during my stats_t > conversion work. The drivers/ tree is littered with stats_t > instances. Not sure how to respond to this, if you're converting all that to stats_t then you're doing it wrong. Most of what you showed should very emphatically not be stats_t.
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