linux-kernel - Re: [PATCH] selftests/mm/cow: Fix the incorrect error handling

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Message-ID: <caaa80e9-16e6-4abb-b198-967c37aeb46f@redhat.com>
Date: Tue, 11 Mar 2025 20:48:17 +0100
From: David Hildenbrand <david@...hat.com>
To: Cyan Yang <cyan.yang@...ive.com>
Cc: akpm@...ux-foundation.org, shuah@...nel.org, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/mm/cow: Fix the incorrect error handling

On 11.03.25 11:38, Cyan Yang wrote:
> On Tue, Mar 11, 2025 at 10:19:32AM +0100, David Hildenbrand wrote:
>> On 11.03.25 03:37, Cyan Yang wrote:
>>> There are two error handlings did not check the correct return value.
>>> This patch will fix them.
>>>
>>> Fixes: f4b5fd6946e244cdedc3bbb9a1f24c8133b2077a ("selftests/vm: anon_cow: THP tests")
>>> Signed-off-by: Cyan Yang <cyan.yang@...ive.com>
>>> ---
>>>    tools/testing/selftests/mm/cow.c | 4 ++--
>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
>>> index 9446673645eb..16fcadc090a4 100644
>>> --- a/tools/testing/selftests/mm/cow.c
>>> +++ b/tools/testing/selftests/mm/cow.c
>>> @@ -876,13 +876,13 @@ static void do_run_with_thp(test_fn fn, enum thp_run thp_run, size_t thpsize)
>>>    		mremap_size = thpsize / 2;
>>>    		mremap_mem = mmap(NULL, mremap_size, PROT_NONE,
>>>    				  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>>> -		if (mem == MAP_FAILED) {
>>> +		if (mremap_mem == MAP_FAILED) {
>>>    			ksft_test_result_fail("mmap() failed\n");
>>>    			goto munmap;
>>>    		}
>>
>> Yes, that check is wrong.
>>
>>>    		tmp = mremap(mem + mremap_size, mremap_size, mremap_size,
>>>    			     MREMAP_MAYMOVE | MREMAP_FIXED, mremap_mem);
>>> -		if (tmp != mremap_mem) {
>>> +		if (tmp == MAP_FAILED) {
>>>    			ksft_test_result_fail("mremap() failed\n");
>>>    			goto munmap;
>>>    		}
>>
>> As Dev says, this one is just fine. Leave it as it is.
>>
> 
> Thank you for the review.
> 
> I agree with you and Dev this is just fine. The reason I prefer to modify it is
> - usually caller checks the return value directly and "tmp == mremap_mem"
> should be determined by "mremap".
> 
> If you still prefer to leave it as it is, I will send out the v2 to remove it.

Yes, leave it as is. This does not belong in this fix for a real error 
checking problem. Thanks!

-- 
Cheers,

David / dhildenb