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

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Date:   Mon, 21 Nov 2016 16:44:28 +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 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.

Regards,
Boqun

> +		if (unlikely(val == UINT_MAX))
> +			return;
> +
> +		new = val + 1;
> +		old = atomic_cmpxchg_relaxed(&r->refs, val, new);
> +		if (old == val)
> +			break;
> +
> +		val = old;
> +	}
> +
> +	WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
> +}
[...]

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