linux-kernel - Re: [PATCH v3 1/3] tracing: Change STR_VAR_MAX

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Message-ID: <75577192da2769b982b748305ad5609d94bd9bcf.camel@kernel.org>
Date:   Fri, 02 Oct 2020 17:04:46 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     axelrasmussen@...gle.com, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] tracing: Change STR_VAR_MAX_LEN

Hi Steve,

On Fri, 2020-10-02 at 15:44 -0400, Steven Rostedt wrote:
> On Thu,  1 Oct 2020 16:46:44 -0500
> Tom Zanussi <zanussi@...nel.org> wrote:
> 
> > 32 is too small for this value, and anyway it makes more sense to
> > use
> > MAX_FILTER_STR_VAL, as this is also the value used for variable-
> > length
> > __strings.
> > 
> > Tested-by: Axel Rasmussen <axelrasmussen@...gle.com>
> > Signed-off-by: Tom Zanussi <zanussi@...nel.org>
> > ---
> >  kernel/trace/trace_synth.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_synth.h
> > b/kernel/trace/trace_synth.h
> > index ac35c45207c4..5166705d1556 100644
> > --- a/kernel/trace/trace_synth.h
> > +++ b/kernel/trace/trace_synth.h
> > @@ -7,7 +7,7 @@
> >  #define SYNTH_SYSTEM		"synthetic"
> >  #define SYNTH_FIELDS_MAX	32
> >  
> > -#define STR_VAR_LEN_MAX		32 /* must be multiple of
> > sizeof(u64) */
> > +#define STR_VAR_LEN_MAX		MAX_FILTER_STR_VAL /* must be
> > multiple of sizeof(u64) */
> 
> Hmm, this requirement is now passed to MAX_FILTER_STR_VAL, but
> there's no
> mention of it there. I guess we should have a
> 
> 	BUILD_BUG_ON(STR_VAR_LEN_MAX & (sizeof(u64) - 1));
> 
> in C code somewhere.

Good point.  I'll add that in the next version.

Thanks,

Tom