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Date: Mon, 21 Nov 2016 16:44:28 +0800
From: Boqun Feng <boqun.feng@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
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        "dave@progbits.org" <dave@progbits.org>,
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Subject: Re: [RFC][PATCH 7/7] kref: Implement using refcount_t
Message-ID: <20161121084428.GG5227@tardis.cn.ibm.com>
References: <20161114173946.501528675@infradead.org>
 <20161114174446.832175072@infradead.org>
 <2236FBA76BA1254E88B949DDB74E612B41C148C4@IRSMSX102.ger.corp.intel.com>
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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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