Re: [PATCH] mm/damon/tests/vaddr-kunit: don't use mas_lock for MM_MT_FLAGS-initialized maple tree

[Guenter Roeck <linux@roeck-us.net>]

On 9/3/24 17:58, SeongJae Park 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

Just in case you need to resend: s/celar/clear/

>>> 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?
> 

Correct. I don't see those messages with your patch. From my perspective, this is

Tested-by: Guenter Roeck <linux@roeck-us.net>

Thanks,
Guenter