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

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Message-ID: <5a4e5058-2b5c-4c65-9811-66bf68128583@paulmck-laptop>
Date:   Mon, 20 Mar 2023 09:58:11 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Douglas RAILLARD <douglas.raillard@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "open list:TRACING" <linux-kernel@...r.kernel.org>,
        "open list:TRACING" <linux-trace-kernel@...r.kernel.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

On Mon, Mar 20, 2023 at 11:20:15AM -0400, Steven Rostedt wrote:
> 
> [ 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()")

Thank you, Steve!

With those fixes, and with an ack or better from Steve, I will be happy
to pull this in to -rcu.  How urgent is this?  The default destination
would be the v6.5 merge window (not the upcoming one, but the one after
that), so if you need it sooner, please let me know.

							Thanx, Paul

> 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)
>