linux-kernel - Re: [PATCH] mm/damon/tests/vaddr-kunit: don't use mas_lock for MM_MT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <78880ac2-f7fe-4dc1-b2cb-25942fb0cacf@roeck-us.net>
Date: Wed, 4 Sep 2024 09:58:20 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, SeongJae Park
 <sj@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 David Hildenbrand <david@...hat.com>,
 Brendan Higgins <brendanhiggins@...gle.com>, David Gow
 <davidgow@...gle.com>, damon@...ts.linux.dev, linux-mm@...ck.org,
 kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/damon/tests/vaddr-kunit: don't use mas_lock for
 MM_MT_FLAGS-initialized maple tree

On 9/3/24 20:36, Liam R. Howlett wrote:
> * Guenter Roeck <linux@...ck-us.net> [240903 22:38]:
>> On 9/3/24 19:31, Liam R. Howlett wrote:
>>> * SeongJae Park <sj@...nel.org> [240903 21:18]:
>>>> On Tue,  3 Sep 2024 17:58:15 -0700 SeongJae Park <sj@...nel.org> wrote:
>>>>
>>>>> On Tue, 3 Sep 2024 20:48:53 -0400 "Liam R. Howlett" <Liam.Howlett@...cle.com> wrote:
>>>>>
>>>>>> * SeongJae Park <sj@...nel.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?
> 

You should find everything needed to reproduce the problem at
http://server.roeck-us.net/qemu/damon/

Please let me know if you need anything else.

Thanks,
Guenter