linux-kernel - Re: [PATCH] perf probe: Fix --line option behavior

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Date:	Tue, 1 Apr 2014 07:21:44 +0000
From:	Namhyung Kim <namhyung@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] perf probe: Fix --line option behavior

Hi Masami,

(Also adding Jiri in CC and changing email of acme)

On Tue, Apr 1, 2014 at 5:01 AM, Masami Hiramatsu
<masami.hiramatsu.pt@...achi.com> wrote:
> (2014/04/01 13:47), Namhyung Kim wrote:
>> The commit 5a62257a3ddd1 ("perf probe: Replace line_list with
>> intlist") replaced line_list to intlist but it has a problem that if a
>> same line was added again, it'd return -EEXIST rather than 1.
>
> Ah, right! that's a different behavior.
>
>> Since line_range_walk_cb() only checks the result being negative, it
>> resulted in failure or segfault sometimes.
>
> Could you give me an example input of the segfault? I'd like to trace
> it down.

Just used current acme/perf/core.

$ git log -1
commit 28b5724a61cc9d84f2cbef6675e8a85ae4b1bc57
Author: Arnaldo Carvalho de Melo <acme@...hat.com>
Date:   Thu Mar 27 17:36:14 2014 -0300

    MAINTAINERS: Change e-mail to kernel.org one

    Leaving ghostprotocols.net for old networking stuff.

...

$ perf --version
perf version 3.14.rc6.g28b572

$ perf probe -x ./perf -v -L map__load
Open Debuginfo file: /home/namhyung/project/linux/tools/perf/perf
fname: util/map.c, lineno:153
New line range: 153 to 2147483647
path: (null)
Segmentation fault (core dumped)


It seems like find_line_range_by_line() called for multiple times,
line_range_walk_cb returns 0 at first but as line_range_add_line()
returns -EEXIST, it freed lr->path and __show_line_range() ended up
accessing to NULL path.


(gdb) bt
#0  get_real_path (new_path=0x839ff8 <params+9272>,
    comp_dir=0x1f994f0 "/home/namhyung/project/linux/tools/perf",
    raw_path=0x0) at util/probe-event.c:518
#1  __show_line_range (module=<optimized out>, lr=0x839fd8 <params+9240>)
    at util/probe-event.c:641
#2  show_line_range (lr=lr@...ry=0x839fd8 <params+9240>,
    module=<optimized out>) at util/probe-event.c:699
#3  0x000000000044667b in __cmd_probe (argc=<optimized out>,
    argv=argv@...ry=0x7fff7a770ba0, prefix=<optimized out>)
    at builtin-probe.c:465
#4  0x00000000004469f4 in cmd_probe (argc=<optimized out>,
    argv=0x7fff7a770ba0, prefix=<optimized out>) at builtin-probe.c:520
#5  0x00000000004241b5 in run_builtin (p=p@...ry=0x7ebde0 <commands+384>,
    argc=argc@...ry=6, argv=argv@...ry=0x7fff7a770ba0) at perf.c:319
#6  0x0000000000423a29 in handle_internal_command (argv=0x7fff7a770ba0,
    argc=6) at perf.c:376
#7  run_argv (argv=0x7fff7a7709a0, argcp=0x7fff7a7709ac) at perf.c:420
#8  main (argc=6, argv=0x7fff7a770ba0) at perf.c:529


Thanks,
Namhyung
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