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

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Message-ID: <30458.1504541309@warthog.procyon.org.uk>
Date:   Mon, 04 Sep 2017 17:08:29 +0100
From:   David Howells <dhowells@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     dhowells@...hat.com, 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

Christoph Hellwig <hch@...radead.org> 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)

Which bit are you objecting to?  Wanting to use a refcount_t with 1 to
represent an otherwise-unreferenced object sat in a cache?  Or wanting to
display accurate usage counts when tracing gets and puts of objects?

David