linux-kernel - Re: [PATCH] rcu: Fix rcu_torture

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Message-ID: <20230320112015.2271da9c@gandalf.local.home>
Date:   Mon, 20 Mar 2023 11:20:15 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Douglas RAILLARD <douglas.raillard@....com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org (open list:TRACING),
        linux-trace-kernel@...r.kernel.org (open list:TRACING),
        "Paul E. McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>, rcu@...r.kernel.org
Subject: Re: [PATCH] rcu: Fix rcu_torture_read ftrace event


[ Wondering why this didn't get picked up in v6.3-rc3, I see that the
  maintainers of RCU were not Cc'd :-( ]

This is a bug that will cause unwanted results. I have a patch that will not
let the kernel build when code like this is added.

  https://patchwork.kernel.org/project/linux-trace-kernel/patch/20230309221302.642e82d9@gandalf.local.home/

( The kernel robot even failed when applying the above patch, because it
  caught the code that this patch fixes )

On Mon,  6 Mar 2023 12:27:43 +0000
Douglas RAILLARD <douglas.raillard@....com> wrote:

> From: Douglas Raillard <douglas.raillard@....com>
> 
> Fix the rcutorturename field so that its size is correctly reported in
> the text format embedded in trace.dat files. As it stands, it is
> reported as being of size 1:

And that the offsets of the following fields will be incorrect as well.

> 
>     field:char rcutorturename[8];   offset:8;       size:1; signed:0;
> 

Please add:

Cc: stable@...r.kernel.org
Fixes: 04ae87a52074e ("ftrace: Rework event_create_dir()")

Thanks,

-- Steve

> Signed-off-by: Douglas Raillard <douglas.raillard@....com>
> ---
>  include/trace/events/rcu.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
> index 90b2fb0292cb..012fa0d171b2 100644
> --- a/include/trace/events/rcu.h
> +++ b/include/trace/events/rcu.h
> @@ -768,7 +768,7 @@ TRACE_EVENT_RCU(rcu_torture_read,
>  	TP_ARGS(rcutorturename, rhp, secs, c_old, c),
>  
>  	TP_STRUCT__entry(
> -		__field(char, rcutorturename[RCUTORTURENAME_LEN])
> +		__array(char, rcutorturename, RCUTORTURENAME_LEN)
>  		__field(struct rcu_head *, rhp)
>  		__field(unsigned long, secs)
>  		__field(unsigned long, c_old)