linux-kernel - Re: [RFC][PATCH] locking/refcount: Provide _

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Message-ID: <4041520.1596055297@warthog.procyon.org.uk>
Date:   Wed, 29 Jul 2020 21:41:37 +0100
From:   David Howells <dhowells@...hat.com>
To:     peterz@...radead.org
Cc:     dhowells@...hat.com, Kees Cook <keescook@...omium.org>,
        Xiaoming Ni <nixiaoming@...wei.com>,
        David Windsor <dwindsor@...il.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Paul Moore <paul@...l-moore.com>, edumazet@...gle.com,
        paulmck@...nel.org, shakeelb@...gle.com,
        James Morris <jamorris@...ux.microsoft.com>,
        alex.huangjianhui@...wei.com, dylix.dailei@...wei.com,
        chenzefeng2@...wei.com, linux-kernel@...r.kernel.org,
        Will Deacon <will@...nel.org>
Subject: Re: [RFC][PATCH] locking/refcount: Provide __refcount API to obtain the old value

peterz@...radead.org wrote:

> I'm not entirely sure what you mean with interpret, provided you don't
> trigger a refcount fail, the number will be just what you expect and
> would get from refcount_read(). If you do trigger a fail, you'll get a
> negative value.

That's fine.  I seem to remember talk about the possibility that the number
wouldn't necessarily bottom out at zero - for instance if it was arranged such
that the overflow flag was set on an overflow or underflow so that it could be
trapped on (using INTO or TRAPV, for example).

David