linux-kernel - AW: [PATCH RT RFC v4 1/8] add generalized priority-inheritance interface

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Date:	Sat, 16 Aug 2008 17:32:55 +0200
From:	"Matthias Behr" <linux@...ehr.de>
To:	"'Gregory Haskins'" <ghaskins@...ell.com>
Cc:	<linux-kernel@...r.kernel.org>, <linux-rt-users@...r.kernel.org>,
	<gregory.haskins@...il.com>, <mingo@...e.hu>,
	<David.Holmes@....com>, <jkacur@...il.com>,
	<paulmck@...ux.vnet.ibm.com>, <peterz@...radead.org>,
	<tglx@...utronix.de>, <rostedt@...dmis.org>
Subject: AW: [PATCH RT RFC v4 1/8] add generalized priority-inheritance interface

Hi Greg,

I got a few review comments/questions. Pls see below.

Best Regards,
Matthias

P.S. I'm a kernel newbie so don't hesitate to tell me if I'm wrong ;-)

> +/**
> + * pi_sink_init - initialize a pi_sink before use
> + * @sink: a sink context
> + * @ops: pointer to an pi_sink_ops structure
> + */
> +static inline void
> +pi_sink_init(struct pi_sink *sink, struct pi_sink_ops *ops)
> +{
> +	atomic_set(&sink->refs, 0);
> +	sink->ops = ops;
> +}

Shouldn't ops be tested for 0 here? (ASSERT/BUG_ON/...) (get's dereferenced later quite often in the form "if (sink->ops->...)".

> +/**
> + * pi_sink_put - down the reference count, freeing the sink if 0
> + * @node: the node context
> + * @flags: optional flags to modify behavior.  Reserved, must be 0.
> + *
> + * Returns: none
> + */
> +static inline void
> +pi_sink_put(struct pi_sink *sink, unsigned int flags)
> +{
> +	if (atomic_dec_and_test(&sink->refs)) {
> +		if (sink->ops->free)
> +			sink->ops->free(sink, flags);
> +	}
> +}

Shouldn't the atomic/locked part cover the ...->free(...) as well? A pi_get right after the atomic_dec_and_test but before the free() could lead to a free() with refs>0?



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