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

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

[SeongJae Park]

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.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net
Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator")
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/tests/vaddr-kunit.h | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
index 83626483f82b..c6c7e0e0ab07 100644
--- a/mm/damon/tests/vaddr-kunit.h
+++ b/mm/damon/tests/vaddr-kunit.h
@@ -17,23 +17,19 @@
 static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas,
 			ssize_t nr_vmas)
 {
-	int i, ret = -ENOMEM;
+	int i;
 	MA_STATE(mas, mt, 0, 0);
 
 	if (!nr_vmas)
 		return 0;
 
-	mas_lock(&mas);
 	for (i = 0; i < nr_vmas; i++) {
 		mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1);
 		if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL))
-			goto failed;
+			return -ENOMEM;
 	}
 
-	ret = 0;
-failed:
-	mas_unlock(&mas);
-	return ret;
+	return 0;
 }
 
 /*
-- 
2.39.2

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

[Liam R. Howlett]

* 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.  We need a lock
and to use the lock for writes.

I'd suggest using different flags so the spinlock is used.

> 
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net
> Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator")
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>  mm/damon/tests/vaddr-kunit.h | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
> index 83626483f82b..c6c7e0e0ab07 100644
> --- a/mm/damon/tests/vaddr-kunit.h
> +++ b/mm/damon/tests/vaddr-kunit.h
> @@ -17,23 +17,19 @@
>  static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas,
>  			ssize_t nr_vmas)
>  {
> -	int i, ret = -ENOMEM;
> +	int i;
>  	MA_STATE(mas, mt, 0, 0);
>  
>  	if (!nr_vmas)
>  		return 0;
>  
> -	mas_lock(&mas);
>  	for (i = 0; i < nr_vmas; i++) {
>  		mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1);
>  		if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL))
> -			goto failed;
> +			return -ENOMEM;
>  	}
>  
> -	ret = 0;
> -failed:
> -	mas_unlock(&mas);
> -	return ret;
> +	return 0;
>  }
>  
>  /*
> -- 
> 2.39.2
> 

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

[SeongJae Park]

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?


Thanks,
SJ

> 
> > 
> > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net
> > Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator")
> > Signed-off-by: SeongJae Park <sj@kernel.org>
> > ---
> >  mm/damon/tests/vaddr-kunit.h | 10 +++-------
> >  1 file changed, 3 insertions(+), 7 deletions(-)
> > 
> > diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
> > index 83626483f82b..c6c7e0e0ab07 100644
> > --- a/mm/damon/tests/vaddr-kunit.h
> > +++ b/mm/damon/tests/vaddr-kunit.h
> > @@ -17,23 +17,19 @@
> >  static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas,
> >  			ssize_t nr_vmas)
> >  {
> > -	int i, ret = -ENOMEM;
> > +	int i;
> >  	MA_STATE(mas, mt, 0, 0);
> >  
> >  	if (!nr_vmas)
> >  		return 0;
> >  
> > -	mas_lock(&mas);
> >  	for (i = 0; i < nr_vmas; i++) {
> >  		mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1);
> >  		if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL))
> > -			goto failed;
> > +			return -ENOMEM;
> >  	}
> >  
> > -	ret = 0;
> > -failed:
> > -	mas_unlock(&mas);
> > -	return ret;
> > +	return 0;
> >  }
> >  
> >  /*
> > -- 
> > 2.39.2
> >

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

[SeongJae Park]

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?

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.

FYI, I ended up writing v1 to simply remove lock usage based on my humble
understanding of the documetnation.

    The maple tree uses a spinlock by default, but external locks can be used for
    tree updates as well.  To use an external lock, the tree must be initialized
    with the ``MT_FLAGS_LOCK_EXTERN flag``, this is usually done with the
    MTREE_INIT_EXT() #define, which takes an external lock as an argument.

(from Documentation/core-api/maple_tree.rst)

I was thinking the fact that the test code is executed in single thread is same
to use of external lock.  I will be happy to learn if I missed something.


Thanks,
SJ

> 
> 
> Thanks,
> SJ
> 
> > 
> > > 
> > > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > > Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net
> > > Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator")
> > > Signed-off-by: SeongJae Park <sj@kernel.org>
> > > ---
> > >  mm/damon/tests/vaddr-kunit.h | 10 +++-------
> > >  1 file changed, 3 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
> > > index 83626483f82b..c6c7e0e0ab07 100644
> > > --- a/mm/damon/tests/vaddr-kunit.h
> > > +++ b/mm/damon/tests/vaddr-kunit.h
> > > @@ -17,23 +17,19 @@
> > >  static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas,
> > >  			ssize_t nr_vmas)
> > >  {
> > > -	int i, ret = -ENOMEM;
> > > +	int i;
> > >  	MA_STATE(mas, mt, 0, 0);
> > >  
> > >  	if (!nr_vmas)
> > >  		return 0;
> > >  
> > > -	mas_lock(&mas);
> > >  	for (i = 0; i < nr_vmas; i++) {
> > >  		mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1);
> > >  		if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL))
> > > -			goto failed;
> > > +			return -ENOMEM;
> > >  	}
> > >  
> > > -	ret = 0;
> > > -failed:
> > > -	mas_unlock(&mas);
> > > -	return ret;
> > > +	return 0;
> > >  }
> > >  
> > >  /*
> > > -- 
> > > 2.39.2
> > >

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

[Guenter Roeck]

On 9/3/24 18:18, SeongJae Park wrote:
> 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?
> 
> 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.
> 
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.

Guenter

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

[Liam R. Howlett]

* Guenter Roeck <linux@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 <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?
> > 
> > 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

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

[SeongJae Park]

On Tue, 3 Sep 2024 22:43:40 -0400 "Liam R. Howlett" <Liam.Howlett@oracle.com> wrote:

> * Guenter Roeck <linux@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 <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?
> > > 
> > > 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.

Thank you for the nice suggestion with the rationales.  Just posted the v2
following it: https://lore.kernel.org/20240904172931.1284-1-sj@kernel.org

> 
> > > 
> > 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.

Thank you.  I agree that's somewhat we can visit separately.

FYI, I was also unable to reproduce rcu warnings with my v2 patch on my setup.
I will also try to use Guenter's more detailed repro
(https://lore.kernel.org/78880ac2-f7fe-4dc1-b2cb-25942fb0cacf@roeck-us.net).


Thanks,
SJ

> 
> Regards,
> Liam

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

[Liam R. Howlett]

* 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.

> 
> ```
> --- 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.
> 
> FYI, I ended up writing v1 to simply remove lock usage based on my humble
> understanding of the documetnation.
> 
>     The maple tree uses a spinlock by default, but external locks can be used for
>     tree updates as well.  To use an external lock, the tree must be initialized
>     with the ``MT_FLAGS_LOCK_EXTERN flag``, this is usually done with the
>     MTREE_INIT_EXT() #define, which takes an external lock as an argument.
> 
> (from Documentation/core-api/maple_tree.rst)
> 
> I was thinking the fact that the test code is executed in single thread is same
> to use of external lock.  I will be happy to learn if I missed something.
> 
> 
> Thanks,
> SJ
> 
> > 
> > 
> > Thanks,
> > SJ
> > 
> > > 
> > > > 
> > > > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > > > Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net
> > > > Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator")
> > > > Signed-off-by: SeongJae Park <sj@kernel.org>
> > > > ---
> > > >  mm/damon/tests/vaddr-kunit.h | 10 +++-------
> > > >  1 file changed, 3 insertions(+), 7 deletions(-)
> > > > 
> > > > diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
> > > > index 83626483f82b..c6c7e0e0ab07 100644
> > > > --- a/mm/damon/tests/vaddr-kunit.h
> > > > +++ b/mm/damon/tests/vaddr-kunit.h
> > > > @@ -17,23 +17,19 @@
> > > >  static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas,
> > > >  			ssize_t nr_vmas)
> > > >  {
> > > > -	int i, ret = -ENOMEM;
> > > > +	int i;
> > > >  	MA_STATE(mas, mt, 0, 0);
> > > >  
> > > >  	if (!nr_vmas)
> > > >  		return 0;
> > > >  
> > > > -	mas_lock(&mas);
> > > >  	for (i = 0; i < nr_vmas; i++) {
> > > >  		mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1);
> > > >  		if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL))
> > > > -			goto failed;
> > > > +			return -ENOMEM;
> > > >  	}
> > > >  
> > > > -	ret = 0;
> > > > -failed:
> > > > -	mas_unlock(&mas);
> > > > -	return ret;
> > > > +	return 0;
> > > >  }
> > > >  
> > > >  /*
> > > > -- 
> > > > 2.39.2
> > > >

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

[Guenter Roeck]

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.

Guenter

>>
>> ```
>> --- 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.
>>
>> FYI, I ended up writing v1 to simply remove lock usage based on my humble
>> understanding of the documetnation.
>>
>>      The maple tree uses a spinlock by default, but external locks can be used for
>>      tree updates as well.  To use an external lock, the tree must be initialized
>>      with the ``MT_FLAGS_LOCK_EXTERN flag``, this is usually done with the
>>      MTREE_INIT_EXT() #define, which takes an external lock as an argument.
>>
>> (from Documentation/core-api/maple_tree.rst)
>>
>> I was thinking the fact that the test code is executed in single thread is same
>> to use of external lock.  I will be happy to learn if I missed something.
>>
>>
>> Thanks,
>> SJ
>>
>>>
>>>
>>> Thanks,
>>> SJ
>>>
>>>>
>>>>>
>>>>> Reported-by: Guenter Roeck <linux@roeck-us.net>
>>>>> Closes: https://lore.kernel.org/1453b2b2-6119-4082-ad9e-f3c5239bf87e@roeck-us.net
>>>>> Fixes: d0cf3dd47f0d ("damon: convert __damon_va_three_regions to use the VMA iterator")
>>>>> Signed-off-by: SeongJae Park <sj@kernel.org>
>>>>> ---
>>>>>   mm/damon/tests/vaddr-kunit.h | 10 +++-------
>>>>>   1 file changed, 3 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
>>>>> index 83626483f82b..c6c7e0e0ab07 100644
>>>>> --- a/mm/damon/tests/vaddr-kunit.h
>>>>> +++ b/mm/damon/tests/vaddr-kunit.h
>>>>> @@ -17,23 +17,19 @@
>>>>>   static int __link_vmas(struct maple_tree *mt, struct vm_area_struct *vmas,
>>>>>   			ssize_t nr_vmas)
>>>>>   {
>>>>> -	int i, ret = -ENOMEM;
>>>>> +	int i;
>>>>>   	MA_STATE(mas, mt, 0, 0);
>>>>>   
>>>>>   	if (!nr_vmas)
>>>>>   		return 0;
>>>>>   
>>>>> -	mas_lock(&mas);
>>>>>   	for (i = 0; i < nr_vmas; i++) {
>>>>>   		mas_set_range(&mas, vmas[i].vm_start, vmas[i].vm_end - 1);
>>>>>   		if (mas_store_gfp(&mas, &vmas[i], GFP_KERNEL))
>>>>> -			goto failed;
>>>>> +			return -ENOMEM;
>>>>>   	}
>>>>>   
>>>>> -	ret = 0;
>>>>> -failed:
>>>>> -	mas_unlock(&mas);
>>>>> -	return ret;
>>>>> +	return 0;
>>>>>   }
>>>>>   
>>>>>   /*
>>>>> -- 
>>>>> 2.39.2
>>>>>

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

[Liam R. Howlett]

* 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.

Just to be clear, you changed the init flags and kept the mas_lock() and
mas_unlock() ?

Thanks,
Liam

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

[Liam R. Howlett]

* 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

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

[Guenter Roeck]

On 9/3/24 20:36, Liam R. Howlett wrote:
> * 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?
> 

I tested again, and I still see


[    6.233483] ok 4 damon
[    6.234190]     KTAP version 1
[    6.234263]     # Subtest: damon-operations
[    6.234335]     # module: vaddr
[    6.234384]     1..6
[    6.235726]
[    6.235931] =============================
[    6.236018] WARNING: suspicious RCU usage
[    6.236280] 6.11.0-rc6-00029-gda66250b210f-dirty #1 Tainted: G                 N
[    6.236398] -----------------------------
[    6.236474] lib/maple_tree.c:832 suspicious rcu_dereference_check() usage!
[    6.236579]
[    6.236579] other info that might help us debug this:
[    6.236579]
[    6.236738]
[    6.236738] rcu_scheduler_active = 2, debug_locks = 1
[    6.237039] no locks held by kunit_try_catch/208.
[    6.237166]
[    6.237166] stack backtrace:
[    6.237385] CPU: 0 UID: 0 PID: 208 Comm: kunit_try_catch Tainted: G                 N 6.11.0-rc6-00029-gda66250b210f-dirty #1
[    6.237629] Tainted: [N]=TEST
[    6.237714] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[    6.238065] Call Trace:
[    6.238233]  <TASK>
[    6.238547]  dump_stack_lvl+0x9e/0xe0
[    6.239473]  lockdep_rcu_suspicious+0x145/0x1b0
[    6.239621]  mas_walk+0x19f/0x1d0
[    6.239765]  mas_find+0xb5/0x150
[    6.239873]  __damon_va_three_regions+0x7e/0x130
[    6.240039]  damon_test_three_regions_in_vmas+0x1ea/0x480
[    6.240551]  ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10
[    6.240712]  kunit_try_run_case+0x93/0x190
[    6.240850]  ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10
[    6.240990]  kunit_generic_run_threadfn_adapter+0x1c/0x40
[    6.241124]  kthread+0xdd/0x110
[    6.241256]  ? __pfx_kthread+0x10/0x10
[    6.241368]  ret_from_fork+0x2f/0x50
[    6.241468]  ? __pfx_kthread+0x10/0x10
[    6.241573]  ret_from_fork_asm+0x1a/0x30
[    6.241765]  </TASK>
[    6.242180]
[    6.242270] =============================
[    6.242375] WARNING: suspicious RCU usage
[    6.242478] 6.11.0-rc6-00029-gda66250b210f-dirty #1 Tainted: G                 N
[    6.242634] -----------------------------
[    6.242734] lib/maple_tree.c:788 suspicious rcu_dereference_check() usage!
[    6.242955]
[    6.242955] other info that might help us debug this:
[    6.242955]
[    6.243098]
[    6.243098] rcu_scheduler_active = 2, debug_locks = 1
[    6.243215] no locks held by kunit_try_catch/208.
[    6.243331]
[    6.243331] stack backtrace:
[    6.243420] CPU: 0 UID: 0 PID: 208 Comm: kunit_try_catch Tainted: G                 N 6.11.0-rc6-00029-gda66250b210f-dirty #1
[    6.243599] Tainted: [N]=TEST
[    6.243665] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[    6.243844] Call Trace:
[    6.243907]  <TASK>
[    6.243961]  dump_stack_lvl+0x9e/0xe0
[    6.244032]  lockdep_rcu_suspicious+0x145/0x1b0
[    6.244121]  mtree_range_walk+0x2b9/0x350
[    6.244211]  mas_walk+0x107/0x1d0
[    6.244278]  mas_find+0xb5/0x150
[    6.244341]  __damon_va_three_regions+0x7e/0x130
[    6.244445]  damon_test_three_regions_in_vmas+0x1ea/0x480
[    6.244770]  ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10
[    6.244865]  kunit_try_run_case+0x93/0x190
[    6.244952]  ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10
[    6.245044]  kunit_generic_run_threadfn_adapter+0x1c/0x40
[    6.245130]  kthread+0xdd/0x110
[    6.245191]  ? __pfx_kthread+0x10/0x10
[    6.245262]  ret_from_fork+0x2f/0x50
[    6.245326]  ? __pfx_kthread+0x10/0x10
[    6.245394]  ret_from_fork_asm+0x1a/0x30
[    6.245497]  </TASK>
[    6.246605]     # damon_test_three_regions_in_vmas: pass:1 fail:0 skip:0 total:1
[    6.246668]     ok 1 damon_test_three_regions_in_vmas

This is with

diff --git a/mm/damon/vaddr-test.h b/mm/damon/vaddr-test.h
index 83626483f82b..a339d117150f 100644
--- a/mm/damon/vaddr-test.h
+++ b/mm/damon/vaddr-test.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_flags(&mm.mm_mt, MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU);
         if (__link_vmas(&mm.mm_mt, vmas, ARRAY_SIZE(vmas)))
                 kunit_skip(test, "Failed to create VMA tree");

I'll put it all together and make it available, but that will have to wait until
tomorrow.

Thanks,
Guenter

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

[Liam R. Howlett]

* Guenter Roeck <linux@roeck-us.net> [240904 00:27]:
> On 9/3/24 20:36, Liam R. Howlett wrote:
> > * 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?
> > 
> 
> I tested again, and I still see
> 
> 
> [    6.233483] ok 4 damon
> [    6.234190]     KTAP version 1
> [    6.234263]     # Subtest: damon-operations
> [    6.234335]     # module: vaddr
> [    6.234384]     1..6
> [    6.235726]
> [    6.235931] =============================
> [    6.236018] WARNING: suspicious RCU usage
> [    6.236280] 6.11.0-rc6-00029-gda66250b210f-dirty #1 Tainted: G                 N
> [    6.236398] -----------------------------
> [    6.236474] lib/maple_tree.c:832 suspicious rcu_dereference_check() usage!
> [    6.236579]
> [    6.236579] other info that might help us debug this:
> [    6.236579]
> [    6.236738]
> [    6.236738] rcu_scheduler_active = 2, debug_locks = 1
> [    6.237039] no locks held by kunit_try_catch/208.
> [    6.237166]
> [    6.237166] stack backtrace:
> [    6.237385] CPU: 0 UID: 0 PID: 208 Comm: kunit_try_catch Tainted: G                 N 6.11.0-rc6-00029-gda66250b210f-dirty #1
> [    6.237629] Tainted: [N]=TEST
> [    6.237714] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> [    6.238065] Call Trace:
> [    6.238233]  <TASK>
> [    6.238547]  dump_stack_lvl+0x9e/0xe0
> [    6.239473]  lockdep_rcu_suspicious+0x145/0x1b0
> [    6.239621]  mas_walk+0x19f/0x1d0
> [    6.239765]  mas_find+0xb5/0x150
> [    6.239873]  __damon_va_three_regions+0x7e/0x130

This function isn't taking the rcu read lock while iterating the tree.

Try this:

diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index b0e8b361891d..08cfd22b5249 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -126,6 +126,7 @@ static int __damon_va_three_regions(struct mm_struct *mm,
         * If this is too slow, it can be optimised to examine the maple
         * tree gaps.
         */
+       rcu_read_lock();
        for_each_vma(vmi, vma) {
                unsigned long gap;
 
@@ -146,6 +147,7 @@ static int __damon_va_three_regions(struct mm_struct *mm,
 next:
                prev = vma;
        }
+       rcu_read_unlock();
 
        if (!sz_range(&second_gap) || !sz_range(&first_gap))
                return -EINVAL;

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

[Guenter Roeck]

On 9/4/24 12:26, Liam R. Howlett wrote:
> * Guenter Roeck <linux@roeck-us.net> [240904 00:27]:
>> On 9/3/24 20:36, Liam R. Howlett wrote:
>>> * 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?
>>>
>>
>> I tested again, and I still see
>>
>>
>> [    6.233483] ok 4 damon
>> [    6.234190]     KTAP version 1
>> [    6.234263]     # Subtest: damon-operations
>> [    6.234335]     # module: vaddr
>> [    6.234384]     1..6
>> [    6.235726]
>> [    6.235931] =============================
>> [    6.236018] WARNING: suspicious RCU usage
>> [    6.236280] 6.11.0-rc6-00029-gda66250b210f-dirty #1 Tainted: G                 N
>> [    6.236398] -----------------------------
>> [    6.236474] lib/maple_tree.c:832 suspicious rcu_dereference_check() usage!
>> [    6.236579]
>> [    6.236579] other info that might help us debug this:
>> [    6.236579]
>> [    6.236738]
>> [    6.236738] rcu_scheduler_active = 2, debug_locks = 1
>> [    6.237039] no locks held by kunit_try_catch/208.
>> [    6.237166]
>> [    6.237166] stack backtrace:
>> [    6.237385] CPU: 0 UID: 0 PID: 208 Comm: kunit_try_catch Tainted: G                 N 6.11.0-rc6-00029-gda66250b210f-dirty #1
>> [    6.237629] Tainted: [N]=TEST
>> [    6.237714] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
>> [    6.238065] Call Trace:
>> [    6.238233]  <TASK>
>> [    6.238547]  dump_stack_lvl+0x9e/0xe0
>> [    6.239473]  lockdep_rcu_suspicious+0x145/0x1b0
>> [    6.239621]  mas_walk+0x19f/0x1d0
>> [    6.239765]  mas_find+0xb5/0x150
>> [    6.239873]  __damon_va_three_regions+0x7e/0x130
> 
> This function isn't taking the rcu read lock while iterating the tree.
> 
> Try this:
> 
> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> index b0e8b361891d..08cfd22b5249 100644
> --- a/mm/damon/vaddr.c
> +++ b/mm/damon/vaddr.c
> @@ -126,6 +126,7 @@ static int __damon_va_three_regions(struct mm_struct *mm,
>           * If this is too slow, it can be optimised to examine the maple
>           * tree gaps.
>           */
> +       rcu_read_lock();
>          for_each_vma(vmi, vma) {
>                  unsigned long gap;
>   
> @@ -146,6 +147,7 @@ static int __damon_va_three_regions(struct mm_struct *mm,
>   next:
>                  prev = vma;
>          }
> +       rcu_read_unlock();
>   
>          if (!sz_range(&second_gap) || !sz_range(&first_gap))
>                  return -EINVAL;
> 


Yes, that fixes the problem for me.

Thanks,
Guenter

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

[SeongJae Park]

On Wed, 4 Sep 2024 12:56:33 -0700 Guenter Roeck <linux@roeck-us.net> wrote:

> On 9/4/24 12:26, Liam R. Howlett wrote:
> > * Guenter Roeck <linux@roeck-us.net> [240904 00:27]:
> >> On 9/3/24 20:36, Liam R. Howlett wrote:
> >>> * 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]:
[...]
> >>> 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?
> >>>
> >>
> >> I tested again, and I still see
> >>
> >>
> >> [    6.233483] ok 4 damon
> >> [    6.234190]     KTAP version 1
> >> [    6.234263]     # Subtest: damon-operations
> >> [    6.234335]     # module: vaddr
> >> [    6.234384]     1..6
> >> [    6.235726]
> >> [    6.235931] =============================
> >> [    6.236018] WARNING: suspicious RCU usage
> >> [    6.236280] 6.11.0-rc6-00029-gda66250b210f-dirty #1 Tainted: G                 N
> >> [    6.236398] -----------------------------
> >> [    6.236474] lib/maple_tree.c:832 suspicious rcu_dereference_check() usage!
> >> [    6.236579]
> >> [    6.236579] other info that might help us debug this:
> >> [    6.236579]
> >> [    6.236738]
> >> [    6.236738] rcu_scheduler_active = 2, debug_locks = 1
> >> [    6.237039] no locks held by kunit_try_catch/208.
> >> [    6.237166]
> >> [    6.237166] stack backtrace:
> >> [    6.237385] CPU: 0 UID: 0 PID: 208 Comm: kunit_try_catch Tainted: G                 N 6.11.0-rc6-00029-gda66250b210f-dirty #1
> >> [    6.237629] Tainted: [N]=TEST
> >> [    6.237714] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> >> [    6.238065] Call Trace:
> >> [    6.238233]  <TASK>
> >> [    6.238547]  dump_stack_lvl+0x9e/0xe0
> >> [    6.239473]  lockdep_rcu_suspicious+0x145/0x1b0
> >> [    6.239621]  mas_walk+0x19f/0x1d0
> >> [    6.239765]  mas_find+0xb5/0x150
> >> [    6.239873]  __damon_va_three_regions+0x7e/0x130

I was able to reproduce this by further enabling PROVE_LOCKING.

> > 
> > This function isn't taking the rcu read lock while iterating the tree.
> > 
> > Try this:
> > 
> > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> > index b0e8b361891d..08cfd22b5249 100644
> > --- a/mm/damon/vaddr.c
> > +++ b/mm/damon/vaddr.c
> > @@ -126,6 +126,7 @@ static int __damon_va_three_regions(struct mm_struct *mm,
> >           * If this is too slow, it can be optimised to examine the maple
> >           * tree gaps.
> >           */
> > +       rcu_read_lock();
> >          for_each_vma(vmi, vma) {
> >                  unsigned long gap;
> >   
> > @@ -146,6 +147,7 @@ static int __damon_va_three_regions(struct mm_struct *mm,
> >   next:
> >                  prev = vma;
> >          }
> > +       rcu_read_unlock();
> >   
> >          if (!sz_range(&second_gap) || !sz_range(&first_gap))
> >                  return -EINVAL;
> > 
> 
> 
> Yes, that fixes the problem for me.

Thank you for the fix, Liam.  Thank you for the test, Guenter.  I also
confirmed this fix works on my setup.

I posted the fix as a formal patch:
https://lore.kernel.org/20240905001204.1481-1-sj@kernel.org


Thanks,
SJ

> 
> Thanks,
> Guenter

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

[Guenter Roeck]

On 9/3/24 20:36, Liam R. Howlett wrote:
> * 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?
> 

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

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

[Guenter Roeck]

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