linux-kernel - Re: [RFC][PATCH 7/7] kref: Implement using refcount

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Message-ID: <20161121093753.GH5227@tardis.cn.ibm.com>
Date:   Mon, 21 Nov 2016 17:37:53 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Reshetova, Elena" <elena.reshetova@...el.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "arnd@...db.de" <arnd@...db.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "dave@...gbits.org" <dave@...gbits.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 7/7] kref: Implement using refcount_t

On Mon, Nov 21, 2016 at 10:02:23AM +0100, Peter Zijlstra wrote:
> On Mon, Nov 21, 2016 at 04:44:28PM +0800, Boqun Feng wrote:
> > On Fri, Nov 18, 2016 at 12:37:18PM +0100, Peter Zijlstra wrote:
> > [snip]
> > > +
> > > +/*
> > > + * Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
> > > + *
> > > + * Provides no memory ordering, it is assumed the caller already has a
> > > + * reference on the object, will WARN when this is not so.
> > > + */
> > > +static inline void refcount_inc(refcount_t *r)
> > > +{
> > > +	unsigned int old, new, val = atomic_read(&r->refs);
> > > +
> > > +	for (;;) {
> > > +		WARN(!val, "refcount_t: increment on 0; use-after-free.\n");
> > > +
> > 
> > Do we want to put the address of @r into the WARN information? Which
> > could help us locate the problematic object quickly.
> 
> I explicitly didn't do that because printing kernel addresses is
> generally frowned upon. Also, random heap addresses are just that,
> random. In most cases the backtrace is more informative.

Fair enough ;-)

Regards,
Boqun

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