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Subject: Re: [PATCH] perf tools: session: avoid infinite loop
To: Mark Rutland <mark.rutland@arm.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
References: <1442423929-12253-1-git-send-email-mark.rutland@arm.com>
 <20150916205454.GI11551@kernel.org> <20150917154152.GD12808@leverpostej>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
From: Adrian Hunter <adrian.hunter@intel.com>
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Date: Fri, 18 Sep 2015 09:09:16 +0300
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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?