* Guenter Roeck linux@roeck-us.net [240903 22:38]:
On 9/3/24 19:31, Liam R. Howlett wrote:
- SeongJae Park sj@kernel.org [240903 21:18]:
On Tue, 3 Sep 2024 17:58:15 -0700 SeongJae Park sj@kernel.org wrote:
On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" Liam.Howlett@oracle.com wrote:
- SeongJae Park sj@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?
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