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

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Date:	Thu, 07 Jul 2011 11:00:49 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Christoph Lameter <cl@...ux.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 07/01/2011 07:11 AM, Christoph Lameter wrote:

>> +#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.

I do not see the problem here.  If PageSlab(page) is true, we fall
through and do the check for on-free-list, under the slab_lock().

We only return error if it is on the free list.  Would these pages
waiting on the RCU interval show up as in the free list?

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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