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

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Message-ID: <Z9ASoTIastiD7utL@cyan-mbp>
Date: Tue, 11 Mar 2025 18:38:25 +0800
From: Cyan Yang <cyan.yang@...ive.com>
To: David Hildenbrand <david@...hat.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 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.

> -- 
> Cheers,
> 
> David / dhildenb
>