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

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Message-ID: <20170901220346.GC439@worktop>
Date:   Sat, 2 Sep 2017 00:03:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-afs@...ts.infradead.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 11:50:03PM +0200, Peter Zijlstra wrote:
> > Did you read the other other part of the description?
> > 
> > 	Further, both functions can be used to accurately trace the refcount
> > 	(refcount_inc() followed by refcount_read() can't be considered
> > 	accurate).
> 
> I must admit to having overlooked that. But can we treat the two issues
> separately? They are quite distinct.

So for tracing purposes inc_return/dec_return don't cover the full set.

In particular: inc_not_zero, dec_not_one and dec_and_*lock are not
covered.

dec_if_one I suppose we only care about the success case, in which case
we knew it was one by inference.