linux-kernel - Re: [RFC PATCH v2 05/20] tracing/filters: Optimise cpumask vs cpumask filtering when user mask is a single CPU

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Date:   Sat, 29 Jul 2023 15:34:36 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org, x86@...nel.org, rcu@...r.kernel.org,
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        Yair Podemsky <ypodemsk@...hat.com>
Subject: Re: [RFC PATCH v2 05/20] tracing/filters: Optimise cpumask vs
 cpumask filtering when user mask is a single CPU

On Thu, 20 Jul 2023 17:30:41 +0100
Valentin Schneider <vschneid@...hat.com> wrote:

>  		/* Move along */
>  		i++;
> +
> +		/*
> +		 * Optimisation: if the user-provided mask has a weight of one
> +		 * then we can treat it as a scalar input.
> +		 */
> +		single = cpumask_weight(pred->mask) == 1;
> +		if (single && field->filter_type == FILTER_CPUMASK) {
> +			pred->val = cpumask_first(pred->mask);
> +			kfree(pred->mask);

Don't we need:
			pred->mask = NULL;

here, or the free_predicate() will cause a double free?

-- Steve

> +		}
> +