Re: [PATCH] tracing: Use kstrdup_const() for constant hist field type

[Steven Rostedt]

On Wed, 27 May 2026 10:10:15 +0900
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote:

> On Tue, 26 May 2026 17:51:05 +0800
> Yu Peng <pengyu@xxxxxxxxxx> wrote:
> 
> > The HIST_FIELD_FL_CONST path duplicates the literal "u64" type with
> > kstrdup(), then releases it through kfree_const().
> > 
> > Use kstrdup_const() instead, avoiding the allocation for a .rodata string
> > while keeping the matching free helper.
> >   
> 
> Since we are using kfree_const() to free hist_field->type,
> we can just point it as same as HIST_FIELD_FL_HITCOUNT case.
> 

Agreed.

> Thanks,
> 
> > Signed-off-by: Yu Peng <pengyu@xxxxxxxxxx>
> > ---
> >  kernel/trace/trace_events_hist.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> > index eb2c2bc8bc3d..6ffe9f4720a0 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -1992,7 +1992,7 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
> >  	if (flags & HIST_FIELD_FL_CONST) {
> >  		hist_field->fn_num = HIST_FIELD_FN_CONST;
> >  		hist_field->size = sizeof(u64);
> > -		hist_field->type = kstrdup("u64", GFP_KERNEL);
> > +		hist_field->type = kstrdup_const("u64", GFP_KERNEL);

This can simply be made to point to "u64".

Thanks,

-- Steve

> >  		if (!hist_field->type)
> >  			goto free;
> >  		goto out;
> > -- 
> > 2.43.0  
> 
>