* Guenter Roeck <li...@roeck-us.net> [240903 21:54]: > On 9/3/24 18:18, SeongJae Park wrote: > > On Tue, 3 Sep 2024 17:58:15 -0700 SeongJae Park <s...@kernel.org> wrote: > > > > > On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" > > > <liam.howl...@oracle.com> wrote: > > > > > > > * SeongJae Park <s...@kernel.org> [240903 20:45]: > > > > > 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 celar when spinlock debugging is turned on, since it > > > > > reports spinlock bad magic bug. Fix the issue by not using the > > > > > mt_lock > > > > > as promised. > > > > > > > > You can't do this, lockdep will tell you this is wrong. > > > > > > Hmm, but lockdep was silence on my setup? > > > > > > > We need a lock and to use the lock for writes. > > > > > > This code is executed by a single-thread test code. Do we still need the > > > lock? > > > > > > > > > > > I'd suggest using different flags so the spinlock is used. > > > > > > The reporter mentioned simply dropping MT_FLAGS_LOCK_EXTERN from the flags > > > causes suspicious RCU usage message. May I ask if you have a suggestion > > > of > > > better flags? > > > > I was actually thinking replacing the mt_init_flags() with mt_init(), which > > same to mt_init_flags() with zero flag, like below. > > > > ``` > > --- 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(&mm.mm_mt); > > if (__link_vmas(&mm.mm_mt, vmas, ARRAY_SIZE(vmas))) > > kunit_skip(test, "Failed to create VMA tree"); > > ``` > > > > And just confirmed it also convinces the reproducer. But because I'm > > obviously > > not familiar with maple tree, would like to hear some comments from Liam or > > others first.
Again, I'd use the flags "MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU" because that gets you the gap tracking that may be necessary for tests in the future - it's closer to the MM_MT_FLAGS, so maybe some mm function you use depends on that. > > > Same here. That is why I gave up after trying MT_FLAGS_ALLOC_RANGE and > "MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU". After all, I really don't know what > I am doing and was just playing around ... and there isn't really a good > explanation why initializing the maple tree with MT_FLAGS_ALLOC_RANGE (but not > MT_FLAGS_USE_RCU) would trigger rcu warnings. Thanks, I'll add that to my list of things to do. Regards, Liam