linux-kernel - Re: [for-linus][PATCH 2/5] tracing/uprobe: Fix double perf

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Message-ID: <20200121150605.GT14879@hirez.programming.kicks-ass.net>
Date:   Tue, 21 Jan 2020 16:06:05 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jiri Olsa <jolsa@...nel.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Namhyung Kim <namhyung@...nel.org>,
        Toke Høiland-Jørgensen <thoiland@...hat.com>,
        Jean-Tsung Hsiao <jhsiao@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [for-linus][PATCH 2/5] tracing/uprobe: Fix double perf_event
 linking on multiprobe uprobe

On Tue, Jan 21, 2020 at 02:59:35PM +0000, David Laight wrote:
> From: Peter Zijlstra
> > Sent: 21 January 2020 14:50
> > On Tue, Jan 21, 2020 at 09:38:49AM -0500, Steven Rostedt 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];
> > >  };
> > 
> > Note that this relies on pure 'luck'. If you stick anything <4 bytes in
> > between the list_head and the data member it'll come unstuck real fast.
> 
> Can you fix it by adding an unnamed struct as in:

The trivial fix is like I suggested in the other thread:

	struct trace_uprobe_filter filters[0];

The alternative that Masami-San suggested should also work.