linux-kernel - Re: [PATCH 05/16] perf test: Fix hist testcases when kptr

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Date:	Tue, 15 Dec 2015 12:03:22 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, Namhyung Kim <namhyung@...nel.org>,
	"Jiri Olsa" <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	David Ahern <dsahern@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Arnaldo Carvalho de Melo" <acme@...hat.com>
Subject: Re: [PATCH 05/16] perf test: Fix hist testcases when kptr_restrict
 is on

Hi,

On 2015/12/15 1:44, Arnaldo Carvalho de Melo wrote:
> From: Namhyung Kim <namhyung@...nel.org>
>
> Currently if kptr_restrict is enabled, all hist tests failed with
> segfaults.  This is because machine__create_kernel_maps() in
> setup_fake_machine() failed in that situation, and it called
> machine__delete() on the error path.  But outer callers again called
> machines__exit() causing double free for the host machine.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Link: http://lkml.kernel.org/r/1450062673-22312-1-git-send-email-namhyung@kernel.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>   tools/perf/tests/hists_common.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)

I have a similar patch on this problem at [1][2].

This patch applied solves only half of the problem I seen. Although double
free is gone, in case when kptr_restrict is enabled a normal user still
gets incorrect result. For example:

  $ ./perf test -v 'filtering hist entries'
  25: Test filtering hist entries                              :
  --- start ---
  test child forked, pid 4186
  Cannot create kernel maps
  test child finished with 0
  ---- end ----
  Test filtering hist entries: Ok

The test body doesn't get called at all. I think in this case we'd better
return 'Skip'.

I'd like to send another for it.

[1] 
http://lkml.kernel.org/g/1450089563-122430-2-git-send-email-wangnan0@huawei.com
[2] 
http://lkml.kernel.org/g/1449726768-79624-1-git-send-email-wangnan0@huawei.com

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