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

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Message-ID: <dcd92fb9-1bb0-6797-7031-130d6f4bcaf1@google.com>
Date:   Thu, 21 Sep 2017 12:40:08 -0700
From:   Greg Hackmann <ghackmann@...gle.com>
To:     Shuah Khan <shuahkh@....samsung.com>,
        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>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        linux-tip-commits@...r.kernel.org, Josef Bacik <jbacik@...com>
Subject: Re: [tip:timers/core] kselftests: timers: set-timer-lat: Tweak
 reporting when timer fires early

On 09/20/2017 04:38 PM, Shuah Khan wrote:
> 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
> 
I'm able to reproduce this locally, though I'm not sure it's a 
redirection issue.  28be3f8f48cf ("kselftests: timers: set-timer-lat: 
Add one-shot timer test cases") appears to have a regression where if 
timer_create() fails due to missing CAP_WAKE_ALARM, do_timer() will 
still try to run the test anyway.

Please revert 28be3f8f48cf and verify whether this fixes the problem for 
you.  If so, I'll send a V2 as soon as possible that fixes the issue. 
(Basically, setup_timer() needs a discrete return value for unsupported 
test cases.)

Sorry for the confusion.