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

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Date:   Fri, 22 Jul 2022 16:07:47 +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 16:00, David Hildenbrand wrote:
> 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?
> 

I think you're right that it doesn't work with tmpfile. I do wonder why,
because I'd have thought that it's sufficient for
vma_wants_writenotify() to return "1" due to the
vma_soft_dirty_enabled() check.

Hm ....

-- 
Thanks,

David / dhildenb