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

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Date:	Fri, 17 Jun 2016 12:24:58 +0300
From:	Dmitry Safonov <dsafonov@...tuozzo.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
	<luto@...capital.net>, <tglx@...utronix.de>, <hpa@...or.com>,
	<x86@...nel.org>, <akpm@...ux-foundation.org>,
	<linux-mm@...ck.org>, <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 06/17/2016 11:03 AM, Ingo Molnar 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)
>
> Yeah, so I changed my mind again, I still don't like that the testcase faults on
> old kernels:
>
>  triton:~/tip/tools/testing/selftests/x86> ./test_mremap_vdso_32
>          AT_SYSINFO_EHDR is 0xf7786000
>  [NOTE]  Moving vDSO: [0xf7786000, 0xf7787000] -> [0xf7781000, 0xf7782000]
>  Segmentation fault
>
> How do I know that this testcase is special and that a segmentation fault in this
> case means that I'm running it on a too old kernel and that it's not some other
> unexpected failure in the test?
>
> At minimum please run it behind fork() and catch the -SIGSEGV child exit:
>
>   mremap(0xf7747000, 4096, 4096, MREMAP_MAYMOVE|MREMAP_FIXED, 0xf7742000) = 0xf7742000
>   --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0xf7747be9} ---
>   +++ killed by SIGSEGV +++
>
> and print:
>
>   [FAIL] mremap() of the vDSO does not work on this kernel!
>
> or such.
>
> Ok?

Ok, will do.

Thanks,
Dmitry