linux-kernel - Re: [PATCH v6 0/3] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE

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Message-ID: <20260129193359.08230ac0@gandalf.local.home>
Date: Thu, 29 Jan 2026 19:33:59 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>, Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH v6 0/3] tracing: Guard __DECLARE_TRACE() use of
 __DO_TRACE_CALL() with SRCU-fast

On Tue, 27 Jan 2026 15:18:05 -0800
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> Ah, I get it.  I think.  NMIs, right?
> 
> In your source tree, line 792 of kernel/rcu/srcutree.c is this line of
> code, correct?
> 
> 	WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi());
> 
> If so, could you please try this test with the patch shown at the end
> of this email?
> 

> 
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index c469c708fdd6a..66ba6a2f83d3a 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -789,7 +789,8 @@ void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
>  	struct srcu_data *sdp;
>  
>  	/* NMI-unsafe use in NMI is a bad sign, as is multi-bit read_flavor values. */
> -	WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi());
> +	WARN_ON_ONCE(read_flavor != SRCU_READ_FLAVOR_NMI &&
> +		     read_flavor != SRCU_READ_FLAVOR_FAST && in_nmi());
>  	WARN_ON_ONCE(read_flavor & (read_flavor - 1));
>  
>  	sdp = raw_cpu_ptr(ssp->sda);

It appears to fix the issue.

Tested-by: Steven Rostedt (Google) <rostedt@...dmis.org>

Care to send a formal patch, and I'll add it before the patch that causes
issues.

Thanks,

-- Steve