Hi Xiaomeng,

On Sun, 27 Mar 2022 16:03:45 +0800 Xiaomeng Tong xiam0nd.tong@gmail.com wrote:

The bug is here: KUNIT_EXPECT_EQ(test, r->ar.start, start + i * expected_width); KUNIT_EXPECT_EQ(test, r->ar.end, end);

For the damon_for_each_region(), just like list_for_each_entry(), the list iterator 'drm_crtc' will point to a bogus position containing HEAD if the list is empty or no element is found. This case must be checked before any use of the iterator, otherwise it will lead to a invalid memory access.

We ensure 'damon_va_evenly_split_region()' successes before executing the loop, so the issue cannot occur. That said, I think this patch makes code better to read. Could you please resend this patch after fixing the commit message?

To fix this bug, just mov two KUNIT_EXPECT_EQ() into the loop

s/mov/move

when found.

Cc: stable@vger.kernel.org Fixes: 044cd9750fe01 ("mm/damon/vaddr-test: split a test function having >1024 bytes frame size") Signed-off-by: Xiaomeng Tong xiam0nd.tong@gmail.com

---

mm/damon/vaddr-test.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/damon/vaddr-test.h b/mm/damon/vaddr-test.h index 6a1b9272ea12..98b7a9f54b35 100644 --- a/mm/damon/vaddr-test.h +++ b/mm/damon/vaddr-test.h @@ -281,14 +281,16 @@ static void damon_test_split_evenly_succ(struct kunit *test, KUNIT_EXPECT_EQ(test, damon_nr_regions(t), nr_pieces);

As mentioned above, this will ensure the loop will not result in the bogus pointer problem.

damon_for_each_region(r, t) {

• if (i == nr_pieces - 1)
  

• if (i == nr_pieces - 1) {
  

• 	KUNIT_EXPECT_EQ(test,
  

• 		r->ar.start, start + i * expected_width);
  

• 	KUNIT_EXPECT_EQ(test, r->ar.end, end);
  break;
  

• }
  

  KUNIT_EXPECT_EQ(test, r->ar.start, start + i++ * expected_width); KUNIT_EXPECT_EQ(test, r->ar.end, start + i * expected_width); }

• KUNIT_EXPECT_EQ(test, r->ar.start, start + i * expected_width);
• KUNIT_EXPECT_EQ(test, r->ar.end, end); damon_free_target(t);

} -- 2.17.1

Thanks, SJ