* Guenter Roeck <linux@xxxxxxxxxxxx> [240903 22:38]: > On 9/3/24 19:31, Liam R. Howlett wrote: > > * SeongJae Park <sj@xxxxxxxxxx> [240903 21:18]: > > > On Tue, 3 Sep 2024 17:58:15 -0700 SeongJae Park <sj@xxxxxxxxxx> wrote: > > > > > > > On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx> wrote: > > > > > > > > > * SeongJae Park <sj@xxxxxxxxxx> [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? > > > > That would be the lockdep complaining, so that's good. > > > > > > > > I was actually thinking replacing the mt_init_flags() with mt_init(), which > > > same to mt_init_flags() with zero flag, like below. > > > > Yes. This will use the spinlock which should fix your issue, but it > > will use a different style of maple tree. > > > > Perhaps use MT_FLAGS_ALLOC_RANGE to use the same type of maple tree, if > > you ever add threading you will want the rcu flag as well > > (MT_FLAGS_USE_RCU). > > > > I would recommend those two and just use the spinlock. > > > > I tried that (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU). it also triggers > the suspicious RCU usage message. > I am running ./tools/testing/kunit/kunit.py run '*damon*' --arch x86_64 --raw with: CONFIG_LOCKDEP=y CONFIG_DEBUG_SPINLOCK=y and I don't have any issue with locking in the existing code. How do I recreate this issue? Thanks, Liam
