linux-kernel - Re: [PATCH v3 2/4] srcu: Add srcu_read_lock_fast_notrace() and srcu_read_unlock_fast

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Message-ID: <20250722221100.GA377047@joelbox2>
Date: Tue, 22 Jul 2025 18:11:00 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH v3 2/4] srcu: Add srcu_read_lock_fast_notrace() and
 srcu_read_unlock_fast_notrace()

On Mon, Jul 21, 2025 at 09:24:31AM -0700, Paul E. McKenney wrote:
> This commit adds no-trace variants of the srcu_read_lock_fast() and
> srcu_read_unlock_fast() functions for tracing use.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  include/linux/srcu.h | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index 478c73d067f7d..7a692bf8f99b9 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -282,6 +282,20 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast(struct srcu_struct *
>  	return retval;
>  }
>  
> +/*
> + * Used by tracing, cannot be traced and cannot call lockdep.
> + * See srcu_read_lock_fast() for more information.
> + */
> +static inline struct srcu_ctr __percpu *srcu_read_lock_fast_notrace(struct srcu_struct *ssp)
> +	__acquires(ssp)

Should these also be marked with 'notrace' attribute?

I am not sure what the precedent is, I do see a few examples of 'notrace' and
'inline' in the same function signature though.

Other than that one nit:
Reviewed-by: Joel Fernandes <joelagnelf@...dia.com>

thanks,

 - Joel


> +{
> +	struct srcu_ctr __percpu *retval;
> +
> +	srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_FAST);
> +	retval = __srcu_read_lock_fast(ssp);
> +	return retval;
> +}
> +
>  /**
>   * srcu_down_read_fast - register a new reader for an SRCU-protected structure.
>   * @ssp: srcu_struct in which to register the new reader.
> @@ -394,6 +408,17 @@ static inline void srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ct
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
>  }
>  
> +/*
> + * Used by tracing, cannot be traced and cannot call lockdep.
> + * See srcu_read_unlock_fast() for more information.
> + */
> +static inline void srcu_read_unlock_fast_notrace(struct srcu_struct *ssp,
> +						 struct srcu_ctr __percpu *scp) __releases(ssp)
> +{
> +	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST);
> +	__srcu_read_unlock_fast(ssp, scp);
> +}
> +
>  /**
>   * srcu_up_read_fast - unregister a old reader from an SRCU-protected structure.
>   * @ssp: srcu_struct in which to unregister the old reader.
> -- 
> 2.40.1
>