Re: [PATCH] tracing/uprobe: Fix double perf_event linking on multiprobe uprobe

Masami Hiramatsu
2020-01-20T15:32:30Z

On Mon, 20 Jan 2020 13:40:22 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, Jan 10, 2020 at 10:45:39AM +0900, Masami Hiramatsu wrote:
>
> > diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> > index 4ee703728aec..03e4e180058d 100644
> > --- a/kernel/trace/trace_probe.h
> > +++ b/kernel/trace/trace_probe.h
> > @@ -230,6 +230,7 @@ struct trace_probe_event {
> > struct trace_event_call call;
> > struct list_head files;
> > struct list_head probes;
> > + char data[0];
> > };
>
> Would it make sense to make the above:
>
> struct trace_uprobe_filter filter[0];
>
> instead? That would ensure that alignment is respected. While I think
> the current code works by accident.

Hmm, if we consider the alignment, shouldn't we allocate the structure
with the alignment gap? Currently it just added the
sizeof(struct trace_uprobe_filter) when kzalloc().

In this case, I think we should introduce a new data structure,
trace_uprobe_event.

Thank you,

>
> > @@ -264,6 +263,14 @@ process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,
> > }
> > NOKPROBE_SYMBOL(process_fetch_insn)
> >
> > +static struct trace_uprobe_filter *
> > +trace_uprobe_get_filter(struct trace_uprobe *tu)
> > +{
> > + struct trace_probe_event *event = tu->tp.event;
> > +
> > + return (struct trace_uprobe_filter *)&event->data[0];
> > +}
>
>

--
Masami Hiramatsu <mhiramat@kernel.org>