linux-kernel - Re: [PATCH 2/2] ksefltest: pidfd: Fix wait

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Date:   Fri, 3 Dec 2021 10:03:20 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Christian Brauner <christian.brauner@...ntu.com>,
        Li Zhijian <lizhijian@...fujitsu.com>
Cc:     linux-kselftest@...r.kernel.org, shuah@...nel.org,
        linux-kernel@...r.kernel.org,
        Christian Brauner <christian@...uner.io>,
        Philip Li <philip.li@...el.com>,
        kernel test robot <lkp@...el.com>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 2/2] ksefltest: pidfd: Fix wait_states: Test terminated by
 timeout

On 10/29/21 2:32 AM, Christian Brauner wrote:
> On Fri, Oct 29, 2021 at 10:45:28AM +0800, Li Zhijian wrote:
>> 0Day/LKP observed that the kselftest blocks foever since one of the
>> pidfd_wait doesn't terminate in 1 of 30 runs. After digging into
>> the source, we found that it blocks at:
>> ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WCONTINUED, NULL), 0);
>>
>> we can reproduce it by:
>> $ while true; do make run_tests -C pidfd; done
>>
>> a delay to ensure that the parent can see child process WCONTINUED.
>>
>> CC: Christian Brauner <christian@...uner.io>
>> CC: Shuah Khan <shuah@...nel.org>
>> CC: Philip Li <philip.li@...el.com>
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Li Zhijian <lizhijian@...fujitsu.com>
>> ---
> 
> Not a fan of the usleep() solution but if it fixes it it's fine for
> a test, I think.
> Acked-by: Christian Brauner <christian.brauner@...ntu.com>
> 

I don't like introducing usleep() which will increase the kselftest
run-time. Every little bit adds up if we allow usleep() in tests.

thanks,
-- Shuah