linux-kernel - Re: [PATCHv9 2/2] selftest/x86: add mremap vdso test

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Date:	Fri, 20 May 2016 08:33:04 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Dmitry Safonov <dsafonov@...tuozzo.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Dmitry Safonov <0x7f454c46@...il.com>,
	Shuah Khan <shuahkh@....samsung.com>,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCHv9 2/2] selftest/x86: add mremap vdso test

On Thu, May 19, 2016 at 11:48 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
>
>> Should print on success:
>> [root@...alhost ~]# ./test_mremap_vdso_32
>>       AT_SYSINFO_EHDR is 0xf773f000
>> [NOTE]        Moving vDSO: [f773f000, f7740000] -> [a000000, a001000]
>> [OK]
>> Or segfault if landing was bad (before patches):
>> [root@...alhost ~]# ./test_mremap_vdso_32
>>       AT_SYSINFO_EHDR is 0xf774f000
>> [NOTE]        Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
>> Segmentation fault (core dumped)
>
> So I still think that generating potential segfaults is not a proper way to test a
> new feature. How are we supposed to tell the feature still works? I realize that
> glibc is a problem here - but that doesn't really change the QA equation: we are
> adding new kernel code to help essentially a single application out of tens of
> thousands of applications.
>
> At minimum we should have a robust testcase ...

I think it's robust enough.  It will print "[OK]" and exit with 0 on
success and it will crash on failure.  The latter should cause make
run_tests to fail reliably.

There are some test cases in there that can't avoid crashing on
failure unless they were to fork, fail in a child, and then print some
text in the parent.  That seems like it would be more work than it's
worth.

--Andy