linux-kernel - Re: [RFC PATCH 02/11] refcount: Implement inc/decrement-and-return functions

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Message-ID: <20170904153654.GA4145@infradead.org>
Date:   Mon, 4 Sep 2017 08:36:54 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-afs@...ts.infradead.org,
        Peter Zijlstra <peterz@...radead.org>,
        linux-fsdevel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 02/11] refcount: Implement inc/decrement-and-return
 functions

On Fri, Sep 01, 2017 at 04:41:01PM +0100, David Howells wrote:
> Implement functions that increment or decrement a refcount_t object and
> return the value.  The dec-and-ret function can be used to maintain a
> counter in a cache where 1 means the object is unused, but available and
> the garbage collector can use refcount_dec_if_one() to make the object
> unavailable.  Further, both functions can be used to accurately trace the
> refcount (refcount_inc() followed by refcount_read() can't be considered
> accurate).

Please just use a different interface for that instead of overloading
refcount_t.  The main use case of that type is that it is so simple that
it is hard to get wrong (and have additional checking if things go
wrong)