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Date: Wed, 28 Feb 2024 19:32:20 +0100
From: Borislav Petkov <bp@alien8.de>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] tracepoints: Use WARN() and not WARN_ON() for warnings
Message-ID: <20240228183220.GDZd98NEDTrzZBGdgi@fat_crate.local>
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On Wed, Feb 28, 2024 at 01:31:12PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> There are two WARN_ON*() warnings in tracepoint.h that deal with RCU
> usage. But when they trigger, especially from using a TRACE_EVENT()
> macro, the information is not very helpful and is confusing:
> 
>  ------------[ cut here ]------------
>  WARNING: CPU: 0 PID: 0 at include/trace/events/lock.h:24 lock_acquire+0x2b2/0x2d0
> 
> Where the above warning takes you to:
> 
>  TRACE_EVENT(lock_acquire,  <<<--- line 24 in lock.h
> 
> 	TP_PROTO(struct lockdep_map *lock, unsigned int subclass,
> 		int trylock, int read, int check,
> 		struct lockdep_map *next_lock, unsigned long ip),
> 	[..]
> 
> Change the WARN_ON_ONCE() to WARN_ONCE() and add a string that allows
> someone to search for exactly where the bug happened.
> 
> Reported-by: Borislav Petkov <bp@alien8.de>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  include/linux/tracepoint.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Tested-by: Borislav Petkov (AMD) <bp@alien8.de>

meaning: tested that it really fires:

[    1.196008] Running RCU Tasks wait API self tests
[    1.200227] ------------[ cut here ]------------
[    1.203899] RCU not watching for tracepoint
[    1.203899] WARNING: CPU: 0 PID: 0 at include/trace/events/lock.h:24 lock_acquire+0x2d3/0x300
..

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette