linux-kernel - Re: [patch V2 18/37] rseq: Provide static branch for runtime debugging

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Message-ID: <87bjnt0xh9.ffs@tglx>
Date: Tue, 02 Sep 2025 15:56:18 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Michael Jeanson <mjeanson@...icios.com>, LKML
 <linux-kernel@...r.kernel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Peter Zijlstra <peterz@...radead.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, "Paul E. McKenney"
 <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Paolo Bonzini
 <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, Wei Liu
 <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, x86@...nel.org,
 Arnd Bergmann <arnd@...db.de>, Heiko Carstens <hca@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>, Sven Schnelle
 <svens@...ux.ibm.com>, Huacai Chen <chenhuacai@...nel.org>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [patch V2 18/37] rseq: Provide static branch for runtime debugging

On Mon, Aug 25 2025 at 16:30, Michael Jeanson wrote:
> On 2025-08-23 12:39, Thomas Gleixner wrote:
>> +static int __init rseq_setup_debug(char *str)
>> +{
>> +	bool on;
>> +
>> +	if (kstrtobool(str, &on))
>> +		return -EINVAL;
>> +	rseq_control_debug(on);
>> +	return 0;
>
> Functions used by __setup() have to return '1' to signal that the 
> argument was handled, otherwise you get this in the kernel log:
>
> kernel: Unknown kernel command line parameters "rseq_debug=1", will be 
> passed to user space.

Duh, yes.