linux-kernel - Re: [patch V3 03/12] rseq: Provide static branch for time slice extensions

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Message-ID: <87pla5tnsu.ffs@tglx>
Date: Wed, 29 Oct 2025 22:12:33 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Randy Dunlap <rdunlap@...radead.org>, LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, "Paul E. McKenney" <paulmck@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>, Jonathan Corbet <corbet@....net>,
 Prakash Sangappa <prakash.sangappa@...cle.com>, Madadi Vineeth Reddy
 <vineethr@...ux.ibm.com>, K Prateek Nayak <kprateek.nayak@....com>, Steven
 Rostedt <rostedt@...dmis.org>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>, Arnd Bergmann <arnd@...db.de>,
 linux-arch@...r.kernel.org
Subject: Re: [patch V3 03/12] rseq: Provide static branch for time slice
 extensions

On Wed, Oct 29 2025 at 10:23, Randy Dunlap wrote:
> On 10/29/25 6:22 AM, Thomas Gleixner wrote:
>> +static int __init rseq_slice_cmdline(char *str)
>> +{
>> +	bool on;
>> +
>> +	if (kstrtobool(str, &on))
>> +		return -EINVAL;
>
> The norm for __setup function returns is:
>
> 		return 0;	/* param not handled - will be added to ENV */
> or
> 		return 1;	/* param is handled (anything non-zero) */
>
>
> Anything non-zero means param is handled, so maybe -EINVAL is OK here,
> since return 0 means that the string is added to init's environment.
>
> If the parsing function recognizes the cmdline option string
> (rseq_slice_ext) but the value is invalid, it should pr_error()
> or something like that but still return 1; (IMHO).
> No need to have "rseq_slice_ext=foo" added to init's ENV.
>
> So return -EINVAL is like return 1 in this case.
> IOW it works as needed.  :)

Bah. I hate this logic so much and I never will memorize it.