linux-kernel - Re: [patch V2 21/37] rseq: Make exit debugging static branch based

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Message-ID: <4cb4a688-7c81-4d52-ad38-9d93cbfec1ef@efficios.com>
Date: Tue, 26 Aug 2025 10:23:21 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Peter Zijlstra <peterz@...radead.org>,
 "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 21/37] rseq: Make exit debugging static branch based

On 2025-08-23 12:39, Thomas Gleixner wrote:
> Disconnect it from the config switch and use the static debug branch. This
> is a temporary measure for validating the rework. At the end this check
> needs to be hidden behind lockdep as it has nothing to do with the other
> debug infrastructure, which mainly aids user space debugging by enabling a
> zoo of checks which terminate misbehaving tasks instead of letting them
> keep the hard to diagnose pieces.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

> ---
>   include/linux/rseq_entry.h |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/include/linux/rseq_entry.h
> +++ b/include/linux/rseq_entry.h
> @@ -275,7 +275,7 @@ static __always_inline void rseq_exit_to
>   
>   	rseq_stat_inc(rseq_stats.exit);
>   
> -	if (IS_ENABLED(CONFIG_DEBUG_RSEQ))
> +	if (static_branch_unlikely(&rseq_debug_enabled))
>   		WARN_ON_ONCE(ev->sched_switch);
>   
>   	/*
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com