linux-kernel - Re: [PATCH v2 1/3] tracing: Change STR_VAR_MAX

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Date:   Thu, 01 Oct 2020 16:50:49 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] tracing: Change STR_VAR_MAX_LEN

Hi Axel,

On Wed, 2020-09-30 at 15:45 -0700, Axel Rasmussen wrote:
> I still get the same WARN_ON behavior when trying to use bpftrace.
> But, I spent some time today reading through that call path, and at
> this point I'm convinced that it's the version of bpftrace I'm using
> which is slightly broken, not the kernel in this case. (To be fair,
> I'm trying to use some unreleased tip-of-tree version of it, with
> some
> not-yet-merged patches, and some extra hacks on top of all that, so
> it's not particularly surprising...)
> 
> In my experiments with just the synthetic event + histogram triggers,
> this patchset works as expected for my use case.
> 
> So (for the whole series, not just this one patch):
> 
> Tested-by: Axel Rasmussen <axelrasmussen@...gle.com>

Thanks!

Tom

> 
> On Wed, Sep 30, 2020 at 11:41 AM 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.
> > 
> > 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) */
> > 
> >  struct synth_field {
> >         char *type;
> > --
> > 2.17.1
> >