linux-kernel - Re: [PATCH v2 2/2] slub: Add method to verify memory is not freed.

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Date:	Fri, 1 Jul 2011 09:11:31 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Ben Greear <greearb@...delatech.com>
cc:	penberg@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] slub:  Add method to verify memory is not
 freed.

On Tue, 28 Jun 2011, greearb@...delatech.com wrote:

> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index ad4dd1c..916ce0f 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -302,6 +302,19 @@ extern void *__kmalloc_node_track_caller(size_t, gfp_t, int, unsigned long);
>
>  #endif /* CONFIG_NUMA */
>
> +/**
> + * Calling this on allocated memory will check that the memory
> + * is expected to be in use, and print warnings if not.
> + */
> +#if defined(CONFIG_SLUB) && defined(CONFIG_SLUB_DEBUG)
> +extern bool verify_mem_not_deleted(const void *x);
> +#else
> +static inline bool verify_mem_not_deleted(const void *x)
> +{
> +	return true;
> +}
> +#endif
> +

Why is this in slab.h and not slub_def.h?

> diff --git a/mm/slub.c b/mm/slub.c
> index 3477ce5..f64caca 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2958,6 +2958,42 @@ size_t ksize(const void *object)
>  }
>  EXPORT_SYMBOL(ksize);
>
> +#ifdef CONFIG_SLUB_DEBUG
> +bool verify_mem_not_deleted(const void *x)
> +{
> +	struct page *page;
> +	void *object = (void *)x;
> +	unsigned long flags;
> +	bool rv;
> +
> +	if (unlikely(ZERO_OR_NULL_PTR(x)))
> +		return false;
> +
> +	local_irq_save(flags);
> +
> +	page = virt_to_head_page(x);
> +	if (unlikely(!PageSlab(page))) {
> +		/* maybe it was from stack? */
> +		rv = true;
> +		goto out_unlock;
> +	}

The above check is problematic for slabs that have SLAB_DESTROY_BY_RCU
set. PageSlab(page) may be true to the next rcu interval.
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