linux-kernel - Re: [tip:timers/core] kselftests: timers: set-timer-lat: Tweak reporting when timer fires early

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Message-ID: <bb074fe3-6fca-2250-0c2c-19c0b4afa91d@osg.samsung.com>
Date:   Wed, 20 Sep 2017 17:38:51 -0600
From:   Shuah Khan <shuahkh@....samsung.com>
To:     Prarit Bhargava <prarit@...hat.com>,
        John Stultz <john.stultz@...aro.org>,
        Shuah Khan <shuah@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Richard Cochran <richardcochran@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Stephen Boyd <stephen.boyd@...aro.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        linux-tip-commits@...r.kernel.org, Josef Bacik <jbacik@...com>,
        Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [tip:timers/core] kselftests: timers: set-timer-lat: Tweak
 reporting when timer fires early

On 09/20/2017 06:31 AM, Prarit Bhargava wrote:
> On 09/19/2017 11:36 PM, John Stultz wrote:
>> On Tue, Sep 19, 2017 at 6:02 PM, Shuah Khan <shuah@...nel.org> wrote:
>>> Hi Greg,
>>>
>>> On 08/20/2017 03:56 AM, tip-bot for Greg Hackmann wrote:
>>>> Commit-ID:  a524b1184b8e86141d689fa78ad150fbf2db9b4c
>>>> Gitweb:     http://git.kernel.org/tip/a524b1184b8e86141d689fa78ad150fbf2db9b4c
>>>> Author:     Greg Hackmann <ghackmann@...gle.com>
>>>> AuthorDate: Tue, 25 Jul 2017 14:36:25 -0700
>>>> Committer:  John Stultz <john.stultz@...aro.org>
>>>> CommitDate: Thu, 17 Aug 2017 12:14:54 -0700
>>>>
>>>> kselftests: timers: set-timer-lat: Tweak reporting when timer fires early
>>>>
>>>> Rather than printing an error inside the alarm signal handler, set a
>>>> flag that we check later.  This keeps the test from spamming the console
>>>> every time the alarm fires early.  It also fixes the test exiting with
>>>> error code 0 if this was the only test failure.
>>>>
>>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>>> Cc: Ingo Molnar <mingo@...nel.org>
>>>> Cc: Miroslav Lichvar <mlichvar@...hat.com>
>>>> Cc: Richard Cochran <richardcochran@...il.com>
>>>> Cc: Prarit Bhargava <prarit@...hat.com>
>>>> Cc: Stephen Boyd <stephen.boyd@...aro.org>
>>>> Cc: Shuah Khan <shuah@...nel.org>
>>>> Cc: linux-kselftest@...r.kernel.org
>>>> Signed-off-by: Greg Hackmann <ghackmann@...gle.com>
>>>> Signed-off-by: John Stultz <john.stultz@...aro.org>
>>>
>>> This commit is making the set-timer-lat hang. I reverted this commit
>>> and there is no hang. Could you please take a look and see if this
>>> commit should be reverted.
>>>
>>> make kselftest as well as make -C tools/testing/selftests/timers run_tests
>>> hang.
>>
>> Do you have any specific details as to how the test hangs? (ie: Log
>> data, as in where it might be when it hangs? Any details about the
>> machine?)
>>
>> I'm not seeing it so far in my testing.
>>
> 
> I just ran it here and don't see any issues.  I'll try on a few other boxes
> to make sure.
> 
> # make -C tools/testing/selftests/timers run_tests

John/Prarit,

Thanks for getting back to me. I isolated the problem to redirecting
test output. If I redirect the output it hangs.

./set-timer-lat > /tmp/set-timer-lat 2>&1

it hangs. The reason I am seeing this is because there is a patch
that came in recently to redirect individual test output to a separate
file to make it easier to understand the test results.

Looks like Commits 28be3f8f48cfb3cf024860f042d424cd4824f5f7 and/or
a524b1184b8e86141d689fa78ad150fbf2db9b4c add dependency on stdin/out/err
to the test.

Anyway just an update. It can be reproduced easily. If we have tests
that can't tolerate redirecting output, I might end up dropping the
patch that is in linux-kselftest fixes

fbcab13d2e2511a858590846ac2e2d7cbd830591

So fat set-timer-lat is the only one I found.

thanks,
-- Shuah