linux-kernel - Re: [PATCH v3 2/3] selftests: soft-dirty: Add test for mprotect

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Date:   Fri, 22 Jul 2022 16:00:22 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Nadav Amit <nadav.amit@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v3 2/3] selftests: soft-dirty: Add test for mprotect

On 22.07.22 15:44, Peter Xu wrote:
> On Fri, Jul 22, 2022 at 09:17:34AM +0200, David Hildenbrand wrote:
>> On 21.07.22 20:33, Peter Xu wrote:
>>> Add two soft-diryt test cases for mprotect() on both anon or file.
>>
>> s/soft-diryt/soft-dirty/
> 
> Fixed.
> 
>>
>>>
>>> Signed-off-by: Peter Xu <peterx@...hat.com>
>>> ---
>>>  tools/testing/selftests/vm/soft-dirty.c | 69 ++++++++++++++++++++++++-
>>>  1 file changed, 68 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/tools/testing/selftests/vm/soft-dirty.c b/tools/testing/selftests/vm/soft-dirty.c
>>> index 08ab62a4a9d0..7d93906aa43f 100644
>>> --- a/tools/testing/selftests/vm/soft-dirty.c
>>> +++ b/tools/testing/selftests/vm/soft-dirty.c
>>> @@ -121,13 +121,78 @@ static void test_hugepage(int pagemap_fd, int pagesize)
>>>  	free(map);
>>>  }
>>>  
>>> +static void test_mprotect(int pagemap_fd, int pagesize, bool anon)
>>> +{
>>> +	const char *type[] = {"file", "anon"};
>>> +	const char *fname = "./soft-dirty-test-file";
>>> +	int test_fd;
>>> +	char *map;
>>
>> Instead of fname, unlink, open, close, unlink  you can use a tmpfile
>>
>> FILE *file;
>>
>> file = tmpfile();
>> if (!file) {
>> 	ksft_test_result_fail("tmpfile() failed\n");
>> 	return;
>> }
>> test_fd = fileno(file);
> 
> Note that tmpfile() should by default fetch from /tmp which is very
> possibly a tmpfs afaict.  It's tricky in this special test case since I
> don't think tmpfs can trigger this bug (shmem doesn't define page_mkwrite).
> 

I don't think we need that? SOFTDIRTY tracking enabled should be
sufficient, or what am I missing?

-- 
Thanks,

David / dhildenb