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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Message-ID: <xhsmh3514s4ya.mognet@vschneid.remote.csb>
Date:   Mon, 31 Jul 2023 12:20:13 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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Subject: Re: [RFC PATCH v2 05/20] tracing/filters: Optimise cpumask vs
 cpumask filtering when user mask is a single CPU

On 29/07/23 15:34, Steven Rostedt wrote:
> 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?
>

We do, thanks for spotting this.

> -- Steve
>
>> +		}
>> +