linux-kernel - Re: [PATCH] perf tools: session: avoid infinite loop

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Message-ID: <55FBAA8C.2020703@intel.com>
Date:	Fri, 18 Sep 2015 09:09:16 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Mark Rutland <mark.rutland@....com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] perf tools: session: avoid infinite loop

On 17/09/15 18:41, Mark Rutland wrote:
> Hi,
> 
> On Wed, Sep 16, 2015 at 09:54:54PM +0100, Arnaldo Carvalho de Melo wrote:
>> Em Wed, Sep 16, 2015 at 06:18:49PM +0100, Mark Rutland escreveu:
>>> This has been observed to result in an exit-time hang when counting
>>> rare/unschedulable events with perf record, and can be triggered
>>> artificially with the script below:
>>>
>>> ----
>>> #!/bin/sh
>>> printf "REPRO: launching perf\n";
>>> ./perf record -e software/config=9/ sleep 1 &
>>> PERF_PID=$!;
>>> sleep 0.002;
>>> kill -2 $PERF_PID;
>>> printf "REPRO: waiting for perf (%d) to exit...\n" "$PERF_PID";
>>> wait $PERF_PID;
>>> printf "REPRO: perf exited\n";
>>> ----
>>
>> So, I run it here, without this patch, and get:
>>
>>   [root@zoo ~]# time ./repro.sh 
>>   REPRO: launching perf
>>   REPRO: waiting for perf (766) to exit...
>>   [ perf record: Woken up 1 times to write data ]
>>   [ perf record: Captured and wrote 0.015 MB perf.data ]
>>   REPRO: perf exited
>>   real	0m1.060s
>>   user	0m0.018s
>>   sys	0m0.037s
> 
> [...]
> 
>> What am I doing wrong? Trying to reproduce this before even looking at
>> the patch :-)
> 
> I suspect you have a shinier computer than I do! ;)
> 

I imagine you would also need to contrive not to write any synthesized MMAP
or COMM events i.e. no access to /proc perhaps?

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