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SubjectRe: [PATCH] perf tools: session: avoid infinite loop
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On 18/09/15 18:29, Arnaldo Carvalho de Melo wrote:
> Em Fri, Sep 18, 2015 at 04:18:51PM +0100, Mark Rutland escreveu:
>> On Fri, Sep 18, 2015 at 04:00:18PM +0100, Arnaldo Carvalho de Melo wrote:
>>> After applying your patch it works, had to tweak the commit log to avoid
>>> starting lines with ---, breaks git scripts, also added a commiter log,
>>> check it, patch is below, after the one I used to not process any
>>> samples.
>
>> Sorry for the '---' problem, I'll bear that in mind in future.
>
>> Your commit log looks fine, though I'm slightly confused by the
>> Reported-by line -- did you mean to add that?
>
> Sorry, I mean Tested-by:, will replace, guess i can replace the one for
> Adrian from Cc: to Tested-by too, right?

Yes

>
> - Arnaldo
>
>> Mark.
>>
>>> commit dd486ec4aa33cfca2fd912ef501d49909005de79
>>> Author: Mark Rutland <mark.rutland@arm.com>
>>> Date: Wed Sep 16 18:18:49 2015 +0100
>>>
>>> perf record: Avoid infinite loop at buildid processing with no samples
>>>
>>> If a session contains no events, we can get stuck in an infinite loop in
>>> __perf_session__process_events, with a non-zero file_size and data_offset, but
>>> a zero data_size.
>>>
>>> In this case, we can mmap the entirety of the file (consisting of the file and
>>> attribute headers), and fetch_mmaped_event will correctly refuse to read any
>>> (unmapped and non-existent) event headers. This causes
>>> __perf_session__process_events to unmap the file and retry with the exact same
>>> parameters, getting stuck in an infinite loop.
>>>
>>> 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";
>>> ----
>>>
>>> To avoid this, have __perf_session__process_events bail out early when
>>> the file has no data (i.e. it has no events).
>>>
>>> Commiter note:
>>>
>>> I only managed to reproduce this when setting
>>> /proc/sys/kernel/kptr_restrict to '1' and changing the code to
>>> purposefully not process any samples and no synthesized samples, i.e.
>>> kptr_restrict prevents 'record' from synthesizing the kernel mmaps for
>>> vmlinux + modules and since it is a workload started from perf, we don't
>>> synthesize mmap/comm records for existing threads.
>>>
>>> Adrian Hunter managed to reproduce it in his environment tho.
>>>
>>> Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
>>> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
>>> Cc: Adrian Hunter <adrian.hunter@intel.com>
>>> Cc: Jiri Olsa <jolsa@redhat.com>
>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>> Link: http://lkml.kernel.org/r/1442423929-12253-1-git-send-email-mark.rutland@arm.com
>>> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>>>
>>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
>>> index 8a4537ee9bc3..fc3f7c922f99 100644
>>> --- a/tools/perf/util/session.c
>>> +++ b/tools/perf/util/session.c
>>> @@ -1580,7 +1580,10 @@ static int __perf_session__process_events(struct perf_session *session,
>>> file_offset = page_offset;
>>> head = data_offset - page_offset;
>>>
>>> - if (data_size && (data_offset + data_size < file_size))
>>> + if (data_size == 0)
>>> + goto out;
>>> +
>>> + if (data_offset + data_size < file_size)
>>> file_size = data_offset + data_size;
>>>
>>> ui_progress__init(&prog, file_size, "Processing events...");
>>>
>



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