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Date: Fri, 16 Dec 2016 15:01:58 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Reshetova, Elena" <elena.reshetova@...el.com>
Cc: Liljestrand Hans <ishkamiel@...il.com>,
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	"will.deacon@....com" <will.deacon@....com>,
	Boqun Feng <boqun.feng@...il.com>,
	David Windsor <dwindsor@...il.com>, "aik@...abs.ru" <aik@...abs.ru>,
	"david@...son.dropbear.id.au" <david@...son.dropbear.id.au>
Subject: Re: Conversion from atomic_t to refcount_t: summary of issues

On Fri, Dec 16, 2016 at 12:10:21PM +0000, Reshetova, Elena wrote:

> Is it ok to add at least refcount_inc_if_zero() ? 

Of course not.

> We already have refcount_dec_if_one(), reffcount_dec_not_one() and
> refcount_inc_not_zero(), so this one is the only missing one and would
> greatly help in couple of cases. 

No, its absolutely insane. 0 means its freed, you cannot get another
reference at that point.

If you have code that relies on that, its broken.

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