linux-kernel - Re: A Bug Inquiry in linux/tools/perf/builtin-record.c

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Date:	Mon, 3 Mar 2014 12:10:47 +0800
From:	xiakaixu <xiakaixu@...wei.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	<a.p.zijlstra@...llo.nl>, <paulus@...ba.org>, <mingo@...hat.com>,
	<acme@...stprotocols.net>, <linux-kernel@...r.kernel.org>,
	Huxinwei <huxinwei@...wei.com>, Genghui <hui.geng@...wei.com>,
	<peifeiyue@...wei.com>
Subject: Re: A Bug Inquiry in linux/tools/perf/builtin-record.c

于 2014/2/27 10:53, xiakaixu 写道:
> Hi Namhyung,
> 
> 于 2014/2/26 16:03, Namhyung Kim 写道:
>> Hi xiakaixu,
>>
>>> 于 2014/2/19 9:48, xiakaixu 写道:
>>>> Hi all,
>>>>
>>>> There is a bug found in my work when running "perf record". The basic information
>>>> is here. As we know, perf record is a parent process and the programme traced is
>>>> a child process when running "perf record". Sometimes the child process become
>>>> zombie state and disappear until the parent process is killed. The bug stays in linux/
>>>> tools/perf/builtin-record.c.
>>>> *********************************************************************
>>>> static int __cmd_record(struct perf_record *rec, int argc, const char **argv)
>>>>     ......
>>>> 	if (hits == rec->samples) {
>>>>                          if (done)
>>>>                                  break;
>>>>                          err = poll(evsel_list->pollfd, evsel_list->nr_fds, -1);
>>>>                          waking++;
>>>>                  }
>>>>     ......
>>>> *********************************************************************
>>>> The parent process still call the function
>>>> poll(evsel_list->pollfd, evsel_list->nr_fds, -1) when the child process has exited
>>>> already, which caused a zombie process.
>>>>
>>>> May I have your opinion ?
>>>> Waiting for your reply!
>>
>> Do you have a real bug report based on this?

> yeah, of course we have it, I'll be glad to provide it if necessary.

>>
>> AFAIK perf record installed a signal handler for SIGCHLD so it'll set
>> the 'done' variable when child exits and then break the loop.

> yes, you are right. Though the 'done' varible will be set when child exits,
> there is time gap between "if(done)" statement and "poll(...)" function.
> The 'done' variable won't be judge when child exits in this time gap.
> You know this time gap is instruction level, so this bug is small probability.
> My solution is adding a while(...) statement outside poll(...) function.
>>

>> Thanks,
>> Namhyung
>> .
>>
> 


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