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

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Date:   Mon, 20 Mar 2023 13:36:50 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.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, 20 Mar 2023 09:58:11 -0700
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> 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.

I would like my patch to get in this release, so if you can get it into
this release too (before the next merge window) that would be great. This is
a real bug. User space tooling can not parse this trace event (when it use
to, so it is a regression), and my patch that prevents other trace events
from making the same mistake will make this code as is fail the build.

For this patch:

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

-- 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)  
> >