linux-kernel - Re: [PATCH 2/2] kselftests: mm: Fail the test if userfaultfd syscall isn't found

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Message-ID: <35f21581-71f3-4234-9b03-dd3e3bda664f@linuxfoundation.org>
Date: Thu, 12 Sep 2024 11:28:30 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>
Cc: kernel@...labora.com, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 2/2] kselftests: mm: Fail the test if userfaultfd syscall
 isn't found

On 9/12/24 10:10, Shuah Khan wrote:
> On 9/12/24 04:31, Muhammad Usama Anjum wrote:
>> The userfaultfd is enabled in the config fragment of mm selftest suite.
>> It must always be present. If it isn't present, we should throw error
>> and not just skip. This would have helped us catch the test breakage.
> 
> Please elaborate on this to help understand the what breakage was
> missed.
> 
> Also this commit log doesn't look right to me. syscall() could
> fail for any reason. Do you mean to see skip is incorrect in this
> error leg? Please see comments below.
> 
>> Adding this now to catch the future breakages.
>>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
>> ---
>>   tools/testing/selftests/mm/pagemap_ioctl.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/mm/pagemap_ioctl.c
>> index bcc73b4e805c6..d83dda8edf62c 100644
>> --- a/tools/testing/selftests/mm/pagemap_ioctl.c
>> +++ b/tools/testing/selftests/mm/pagemap_ioctl.c
>> @@ -95,7 +95,7 @@ int init_uffd(void)
>>       uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
>>       if (uffd == -1)
>> -        return uffd;
>> +        ksft_exit_fail_perror("Userfaultfd syscall failed");
> 
> This looks wrong to me - Is missing config the only reason this syscall
> would fail?

It should still skip if __NR_userfaultfd isn't supported on a release
or an architecture.

The real problem seems to be in main():

if (init_uffd())
                 ksft_exit_pass();


Why is this ksft_exit_pass()? Looks like further investigation is
necessary to understand the problem and fix.

thanks,
-- Shuah