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Subject: Re: [PATCH] kmemleak: Do not corrupt the object_list during clean-up
To:     Catalin Marinas <catalin.marinas@arm.com>, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org,
        Marc Dionne <marc.c.dionne@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20191004134624.46216-1-catalin.marinas@arm.com>
From:   Alexey Kardashevskiy <aik@ozlabs.ru>
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Message-ID: <5a75249e-47ee-bb7c-d281-31b385d8bb86@ozlabs.ru>
Date:   Sat, 5 Oct 2019 13:11:10 +1000
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Sender: linux-kernel-owner@vger.kernel.org
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On 04/10/2019 23:46, Catalin Marinas wrote:
> In case of an error (e.g. memory pool too small), kmemleak disables
> itself and cleans up the already allocated metadata objects. However, if
> this happens early before the RCU callback mechanism is available,
> put_object() skips call_rcu() and frees the object directly. This is not
> safe with the RCU list traversal in __kmemleak_do_cleanup().
> 
> Change the list traversal in __kmemleak_do_cleanup() to
> list_for_each_entry_safe() and remove the rcu_read_{lock,unlock} since
> the kmemleak is already disabled at this point. In addition, avoid an
> unnecessary metadata object rb-tree look-up since it already has the
> struct kmemleak_object pointer.
> 
> Fixes: c5665868183f ("mm: kmemleak: use the memory pool for early allocations")
> Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> Reported-by: Marc Dionne <marc.c.dionne@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>


Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>

It not just fixed lockups but brought network speed back to normal but I guess it is because kmemleak disables itself
when CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE=400.

dmesg:
[    0.000000] kmemleak: Memory pool empty, consider increasing CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE
[    0.000000] kmemleak: Cannot allocate a kmemleak_object structure
[    0.000000] kmemleak: Kernel memory leak detector disabled


> ---
>  mm/kmemleak.c | 30 +++++++++++++++++++++---------
>  1 file changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 03a8d84badad..244607663363 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -526,6 +526,16 @@ static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias)
>  	return object;
>  }
>  
> +/*
> + * Remove an object from the object_tree_root and object_list. Must be called
> + * with the kmemleak_lock held _if_ kmemleak is still enabled.
> + */
> +static void __remove_object(struct kmemleak_object *object)
> +{
> +	rb_erase(&object->rb_node, &object_tree_root);
> +	list_del_rcu(&object->object_list);
> +}
> +
>  /*
>   * Look up an object in the object search tree and remove it from both
>   * object_tree_root and object_list. The returned object's use_count should be
> @@ -538,10 +548,8 @@ static struct kmemleak_object *find_and_remove_object(unsigned long ptr, int ali
>  
>  	write_lock_irqsave(&kmemleak_lock, flags);
>  	object = lookup_object(ptr, alias);
> -	if (object) {
> -		rb_erase(&object->rb_node, &object_tree_root);
> -		list_del_rcu(&object->object_list);
> -	}
> +	if (object)
> +		__remove_object(object);
>  	write_unlock_irqrestore(&kmemleak_lock, flags);
>  
>  	return object;
> @@ -1834,12 +1842,16 @@ static const struct file_operations kmemleak_fops = {
>  
>  static void __kmemleak_do_cleanup(void)
>  {
> -	struct kmemleak_object *object;
> +	struct kmemleak_object *object, *tmp;
>  
> -	rcu_read_lock();
> -	list_for_each_entry_rcu(object, &object_list, object_list)
> -		delete_object_full(object->pointer);
> -	rcu_read_unlock();
> +	/*
> +	 * Kmemleak has already been disabled, no need for RCU list traversal
> +	 * or kmemleak_lock held.
> +	 */
> +	list_for_each_entry_safe(object, tmp, &object_list, object_list) {
> +		__remove_object(object);
> +		__delete_object(object);
> +	}
>  }
>  
>  /*
> 

-- 
Alexey