Re: [PATCH 02/22 -v7] Add basic support for gcc profilerinstrumentation

[Peter Zijlstra]

On Tue, 2008-01-29 at 22:15 -0500, Steven Rostedt wrote:

> +int register_mcount_function(struct mcount_ops *ops)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&mcount_func_lock, flags);
> +	ops->next = mcount_list;
> +	/* must have next seen before we update the list pointer */
> +	smp_wmb();

That comment does not explain which race it closes; this is esp
important as there is no paired barrier to give hints.

> +	mcount_list = ops;
> +	/*
> +	 * For one func, simply call it directly.
> +	 * For more than one func, call the chain.
> +	 */
> +	if (ops->next == &mcount_list_end)
> +		mcount_trace_function = ops->func;
> +	else
> +		mcount_trace_function = mcount_list_func;
> +	spin_unlock_irqrestore(&mcount_func_lock, flags);
> +
> +	return 0;
> +}


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