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