linux-kernel - Re: [PATCH] slub: Fix sysfs circular locking dependency

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Date:	Tue, 4 Jan 2011 19:44:37 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Pekka Enberg <penberg@...nel.org>
cc:	linux-kernel@...r.kernel.org,
	Bart Van Assche <bart.vanassche@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency

On Tue, 4 Jan 2011, Pekka Enberg wrote:

> diff --git a/mm/slub.c b/mm/slub.c
> index bec0e35..9831004 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2516,7 +2516,13 @@ void kmem_cache_destroy(struct kmem_cache *s)
>  		}
>  		if (s->flags & SLAB_DESTROY_BY_RCU)
>  			rcu_barrier();
> +		/*
> +		 * The locking order is (1) sysfs internal locks and (2)
> +		 * slub_lock so drop the latter to avoid a deadlock.
> +		 */
> +		up_write(&slub_lock);
>  		sysfs_slab_remove(s);
> +		return;
>  	}
>  	up_write(&slub_lock);
>  }

slub_lock protects slab_state following kmem_cache_init() if caches are 
created/destroyed prior to the sysfs slab initcall setting the global 
variable, so couldn't this leak the kobject if its initialization and add 
was deferred on kmem_cache_create() and added by slab_sysfs_init()?
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