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

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Message-ID: <20170904073020.jrayxderjzchk2g5@hirez.programming.kicks-ass.net>
Date:   Mon, 4 Sep 2017 09:30:20 +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 11:51:53PM +0100, David Howells wrote:
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > 	if (obj) {
> > 	  /* use obj */
> > 	  refcount_dec(&obj->refs); /* should never hit 0 */
> > 	}
> 
> You've missed a bit: We need to tell the gc to run when we reduce the refcount
> to 1:
> 
> 	if (obj) {
> 		...
> 		if (refcount_dec_return(&obj->refs) == 1)
> 			schedule_gc();
> 	}

Ah, so that isn't fundamental to having a GC. But yes if that's your
requirement, then this makes sense.

Please clarify in the Changelog.