linux-kernel - Re: z3fold: suspicious return with spinlock held

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Message-ID: <20170310213419.GD16328@bombadil.infradead.org>
Date:   Fri, 10 Mar 2017 13:34:19 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Alexey Khoroshilov <khoroshilov@...ras.ru>
Cc:     Vitaly Wool <vitalywool@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Streetman <ddstreet@...e.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org
Subject: Re: z3fold: suspicious return with spinlock held

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