z3fold: suspicious return with spinlock held

z3fold: suspicious return with spinlock held

[Alexey Khoroshilov]

Hello!

z3fold_reclaim_page() contains the only return that may
leave the function with pool->lock spinlock held.

669 	spin_lock(&pool->lock);
670 	if (kref_put(&zhdr->refcount, release_z3fold_page)) {
671 		atomic64_dec(&pool->pages_nr);
672 		return 0;
673 	}

May be we need spin_unlock(&pool->lock); just before return?


Found by Linux Driver Verification project (linuxtesting.org).

--
Thank you,
Alexey Khoroshilov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org

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Re: z3fold: suspicious return with spinlock held

[Matthew Wilcox]

On Sat, Mar 11, 2017 at 12:22:12AM +0300, Alexey Khoroshilov wrote:
> Hello!
> 
> z3fold_reclaim_page() contains the only return that may
> leave the function with pool->lock spinlock held.
> 
> 669 	spin_lock(&pool->lock);
> 670 	if (kref_put(&zhdr->refcount, release_z3fold_page)) {
> 671 		atomic64_dec(&pool->pages_nr);
> 672 		return 0;
> 673 	}
> 
> May be we need spin_unlock(&pool->lock); just before return?

I would tend to agree.  sparse warns about this, and also about two
other locking problems ... which I'm not sure are really problems so
much as missing annotations?

mm/z3fold.c:467:35: warning: context imbalance in 'z3fold_alloc' - unexpected unlock
mm/z3fold.c:519:26: warning: context imbalance in 'z3fold_free' - different lock contexts for basic block
mm/z3fold.c:581:12: warning: context imbalance in 'z3fold_reclaim_page' - different lock contexts for basic block

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Re: z3fold: suspicious return with spinlock held

[Alexey Khoroshilov]

On 11.03.2017 00:34, Matthew Wilcox wrote:
> On Sat, Mar 11, 2017 at 12:22:12AM +0300, Alexey Khoroshilov wrote:
>> Hello!
>>
>> z3fold_reclaim_page() contains the only return that may
>> leave the function with pool->lock spinlock held.
>>
>> 669 	spin_lock(&pool->lock);
>> 670 	if (kref_put(&zhdr->refcount, release_z3fold_page)) {
>> 671 		atomic64_dec(&pool->pages_nr);
>> 672 		return 0;
>> 673 	}
>>
>> May be we need spin_unlock(&pool->lock); just before return?
> 
> I would tend to agree.  sparse warns about this, and also about two
> other locking problems ... which I'm not sure are really problems so
> much as missing annotations?
> 
> mm/z3fold.c:467:35: warning: context imbalance in 'z3fold_alloc' - unexpected unlock
> mm/z3fold.c:519:26: warning: context imbalance in 'z3fold_free' - different lock contexts for basic block
> mm/z3fold.c:581:12: warning: context imbalance in 'z3fold_reclaim_page' - different lock contexts for basic block
> 

I also do not see problems in z3fold_alloc() and z3fold_free().
But I am unaware of sparse annotations that can help here.

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Alexey

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Re: z3fold: suspicious return with spinlock held

[vitalywool]

Hi Alexey,

> 10 mars 2017 kl. 22:54 skrev Alexey Khoroshilov <khoroshilov@ispras.ru>:
> 
>> On 11.03.2017 00:34, Matthew Wilcox wrote:
>>> On Sat, Mar 11, 2017 at 12:22:12AM +0300, Alexey Khoroshilov wrote:
>>> Hello!
>>> 
>>> z3fold_reclaim_page() contains the only return that may
>>> leave the function with pool->lock spinlock held.
>>> 
>>> 669    spin_lock(&pool->lock);
>>> 670    if (kref_put(&zhdr->refcount, release_z3fold_page)) {
>>> 671        atomic64_dec(&pool->pages_nr);
>>> 672        return 0;
>>> 673    }
>>> 
>>> May be we need spin_unlock(&pool->lock); just before return?
Looks so, thanks for the pointer. I'm currently commuting but will check it thoroughly tomorrow for sure.

~vitaly 

>> 
>> I would tend to agree.  sparse warns about this, and also about two
>> other locking problems ... which I'm not sure are really problems so
>> much as missing annotations?
>> 
>> mm/z3fold.c:467:35: warning: context imbalance in 'z3fold_alloc' - unexpected unlock
>> mm/z3fold.c:519:26: warning: context imbalance in 'z3fold_free' - different lock contexts for basic block
>> mm/z3fold.c:581:12: warning: context imbalance in 'z3fold_reclaim_page' - different lock contexts for basic block
>> 
> 
> I also do not see problems in z3fold_alloc() and z3fold_free().
> But I am unaware of sparse annotations that can help here.
> 
> --
> Alexey

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