On 9/4/24 10:29, SeongJae Park wrote:

damon_test_three_regions_in_vmas() initializes a maple tree with MM_MT_FLAGS. The flags contains MT_FLAGS_LOCK_EXTERN, which means mt_lock of the maple tree will not be used. And therefore the maple tree initialization code skips initialization of the mt_lock. However, __link_vmas(), which adds vmas for test to the maple tree, uses the mt_lock. In other words, the uninitialized spinlock is used. The problem becomes clear when spinlock debugging is turned on, since it reports spinlock bad magic bug.

Fix the issue by excluding MT_FLAGS_LOCK_EXTERN from the maple tree initialization flags. Note that we don't use empty flags to make it further similar to the usage of mm maple tree, and to be prepared for possible future changes, as suggested by Liam.

Reported-by: Guenter Roeck linux@roeck-us.net Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator") Suggested-by: Liam R. Howlett Liam.Howlett@oracle.com Signed-off-by: SeongJae Park sj@kernel.org

---

Changes from v1 (https://lore.kernel.org/20240904004534.1189-1-sj@kernel.org)

• Keep lock usage and update the initialization flags (Liam)

Not sure I understand how this is better. Is the resulting rcu warning considered to be irrelevant or a separate problem ?

Thanks, Guenter

• Fix a typo: s/celar/clear/ (Guenter)

  mm/damon/tests/vaddr-kunit.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h index 83626483f82b..a339d117150f 100644 --- a/mm/damon/tests/vaddr-kunit.h +++ b/mm/damon/tests/vaddr-kunit.h @@ -77,7 +77,7 @@ static void damon_test_three_regions_in_vmas(struct kunit *test) (struct vm_area_struct) {.vm_start = 307, .vm_end = 330}, };

• mt_init_flags(&mm.mm_mt, MM_MT_FLAGS);

• mt_init_flags(&mm.mm_mt, MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU); if (__link_vmas(&mm.mm_mt, vmas, ARRAY_SIZE(vmas))) kunit_skip(test, "Failed to create VMA tree");