Date:	Fri, 27 Aug 2010 09:12:24 +0300 (EEST)
From:	Hiroshi DOYU <Hiroshi.DOYU@...ia.com>
To:	catalin.marinas@....com
Cc:	linux-kernel@...r.kernel.org, ext-phil.2.carmody@...ia.com,
	linux-omap@...r.kernel.org
Subject: Re: [RFC][PATCH 0/1] kmemleak: Fix false positive with alias

Hi Catalin,

From: Hiroshi DOYU <Hiroshi.DOYU@...ia.com>
Subject: Re: [RFC][PATCH 0/1] kmemleak: Fix false positive with alias
Date: Tue, 10 Aug 2010 18:49:03 +0300 (EEST)

<snip>
>>> The performance impact is indeed pretty high, though some parts of the
>>> code look over-engineered to me (the __scan_block function with a loop
>>> going through an array of two function pointers - I think the compiler
>>> cannot figure out what to inline). You could just extend the
>>> find_and_get_object() to search both trees under a single spinlock
>>> region (as locking also takes time).
>> 
>> Ok, a good point.
> 
> Now there's not much difference with the attached patch, a new version
> of alias.
> 
> / # modprobe kmemleak-special-test use_alias=0
> / # time echo scan > /sys/kernel/debug/kmemleak
> real    0m 2.30s
> user    0m 0.00s
> sys     0m 2.30s
> 
> / # modprobe kmemleak-special-test use_alias=1
> / # time echo scan > /sys/kernel/debug/kmemleak
> real    0m 3.91s
> user    0m 0.00s
> sys     0m 3.91s

It would be nice if you could have some time to take a look at this
patch and give some comments.

> From a5670d69b2cafe85f6f26f6951097210d3b9917f Mon Sep 17 00:00:00 2001
> From: Hiroshi DOYU <Hiroshi.DOYU@...ia.com>
> Date: Thu, 17 Jun 2010 13:36:45 +0300
> Subject: [PATCH 1/1] kmemleak: Fix false positive with address alias
> 
> There is a false positive case that a pointer is calculated by other
> methods than the usual container_of macro. "kmemleak_ignore" can cover
> such a false positive, but it would loose the advantage of memory leak
> detection. This patch allows kmemleak to work with such false
> positives by aliasing of address. A client module can register an
> alias address to an original pointer.
> 
> A typical use case could be the IOMMU pagetable allocation which
> stores pointers to the second level of page tables with some
> conversion, for example, a physical address with attribute bits. Right
> now I don't have other use cases but I hope that there could be some
> that this special scan works with.
> 
> Signed-off-by: Hiroshi DOYU <Hiroshi.DOYU@...ia.com>
> Cc: Phil Carmody <ext-phil.2.carmody@...ia.com>
> ---
>  include/linux/kmemleak.h |    8 ++
>  mm/kmemleak.c            |  208 +++++++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 204 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/kmemleak.h b/include/linux/kmemleak.h
> index 99d9a67..9e2af3a 100644
> --- a/include/linux/kmemleak.h
> +++ b/include/linux/kmemleak.h
> @@ -34,6 +34,8 @@ extern void kmemleak_not_leak(const void *ptr) __ref;
>  extern void kmemleak_ignore(const void *ptr) __ref;
>  extern void kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp) __ref;
>  extern void kmemleak_no_scan(const void *ptr) __ref;
> +extern void kmemleak_add_alias(const void *ptr, const void *new) __ref;
> +extern void kmemleak_unalias(const void *alias) __ref;
>  
>  static inline void kmemleak_alloc_recursive(const void *ptr, size_t size,
>  					    int min_count, unsigned long flags,
> @@ -92,6 +94,12 @@ static inline void kmemleak_erase(void **ptr)
>  static inline void kmemleak_no_scan(const void *ptr)
>  {
>  }
> +static inline void kmemleak_add_alias(const void *ptr, const void *new)
> +{
> +}
> +static inline void kmemleak_unalias(const void *alias)
> +{
> +}
>  
>  #endif	/* CONFIG_DEBUG_KMEMLEAK */
>  
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index 2c0d032..3875cb7 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -157,6 +157,13 @@ struct kmemleak_object {
>  	unsigned long jiffies;		/* creation timestamp */
>  	pid_t pid;			/* pid of the current task */
>  	char comm[TASK_COMM_LEN];	/* executable name */
> +	struct kmemleak_alias *alias;	/* if a pointer is modified */
> +};
> +
> +struct kmemleak_alias {
> +	struct list_head alias_list;
> +	struct prio_tree_node tree_node;
> +	struct kmemleak_object *object;
>  };
>  
>  /* flag representing the memory block allocation status */
> @@ -179,13 +186,18 @@ struct kmemleak_object {
>  static LIST_HEAD(object_list);
>  /* the list of gray-colored objects (see color_gray comment below) */
>  static LIST_HEAD(gray_list);
> +/* the list of objects with alias (see alias comment below) */
> +static LIST_HEAD(alias_list);
>  /* prio search tree for object boundaries */
>  static struct prio_tree_root object_tree_root;
> +/* prio search tree for alias object boundaries */
> +static struct prio_tree_root alias_tree_root;
>  /* rw_lock protecting the access to object_list and prio_tree_root */
>  static DEFINE_RWLOCK(kmemleak_lock);
>  
>  /* allocation caches for kmemleak internal data */
>  static struct kmem_cache *object_cache;
> +static struct kmem_cache *alias_cache;
>  static struct kmem_cache *scan_area_cache;
>  
>  /* set if tracing memory operations is enabled */
> @@ -269,6 +281,8 @@ static void kmemleak_disable(void);
>  	kmemleak_disable();		\
>  } while (0)
>  
> +#define to_address(obj) ((obj)->tree_node.start)
> +
>  /*
>   * Printing of the objects hex dump to the seq file. The number of lines to be
>   * printed is limited to HEX_MAX_LINES to prevent seq file spamming. The
> @@ -369,7 +383,7 @@ static void dump_object_info(struct kmemleak_object *object)
>  	trace.entries = object->trace;
>  
>  	pr_notice("Object 0x%08lx (size %zu):\n",
> -		  object->tree_node.start, object->size);
> +		  to_address(object), object->size);
>  	pr_notice("  comm \"%s\", pid %d, jiffies %lu\n",
>  		  object->comm, object->pid, object->jiffies);
>  	pr_notice("  min_count = %d\n", object->min_count);
> @@ -436,6 +450,8 @@ static void free_object_rcu(struct rcu_head *rcu)
>  		hlist_del(elem);
>  		kmem_cache_free(scan_area_cache, area);
>  	}
> +	if (object->alias)
> +		kmem_cache_free(alias_cache, object->alias);
>  	kmem_cache_free(object_cache, object);
>  }
>  
> @@ -460,12 +476,11 @@ static void put_object(struct kmemleak_object *object)
>  /*
>   * Look up an object in the prio search tree and increase its use_count.
>   */
> -static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias)
> +static struct kmemleak_object *__find_and_get_object(unsigned long ptr, int alias)
>  {
>  	unsigned long flags;
>  	struct kmemleak_object *object = NULL;
>  
> -	rcu_read_lock();
>  	read_lock_irqsave(&kmemleak_lock, flags);
>  	if (ptr >= min_addr && ptr < max_addr)
>  		object = lookup_object(ptr, alias);
> @@ -474,6 +489,75 @@ static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias)
>  	/* check whether the object is still available */
>  	if (object && !get_object(object))
>  		object = NULL;
> +
> +	return object;
> +}
> +
> +static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias)
> +{
> +	struct kmemleak_object *object;
> +
> +	rcu_read_lock();
> +	object = __find_and_get_object(ptr, alias);
> +	rcu_read_unlock();
> +
> +	return object;
> +}
> +
> +static struct kmemleak_object *__find_and_get_alias(unsigned long ptr, int alias)
> +{
> +	struct kmemleak_object *object = NULL;
> +	struct kmemleak_alias *ao = NULL;
> +	struct prio_tree_node *node;
> +	struct prio_tree_iter iter;
> +	unsigned long flags;
> +
> +	read_lock_irqsave(&kmemleak_lock, flags);
> +
> +	prio_tree_iter_init(&iter, &alias_tree_root, ptr, ptr);
> +	node = prio_tree_next(&iter);
> +	if (node) {
> +		ao = prio_tree_entry(node, struct kmemleak_alias, tree_node);
> +		if (!alias && to_address(ao) != ptr) {
> +			kmemleak_warn("Found object by alias");
> +			ao = NULL;
> +		}
> +	}
> +
> +	read_unlock_irqrestore(&kmemleak_lock, flags);
> +
> +	if (ao && get_object(ao->object))
> +		object = ao->object;
> +
> +	return object;
> +}
> +
> +static struct kmemleak_object *find_and_get_alias(unsigned long ptr, int alias)
> +{
> +	struct kmemleak_object *object = NULL;
> +
> +	rcu_read_lock();
> +	object = __find_and_get_alias(ptr, alias);
> +	rcu_read_unlock();
> +
> +	return object;
> +}
> +
> +/*
> + * Try to find object first, and then with alias address if not found.
> + */
> +static struct kmemleak_object *find_and_get_object_with_alias(unsigned long ptr,
> +							      int alias)
> +{
> +	struct kmemleak_object *object = NULL;
> +
> +	rcu_read_lock();
> +
> +	object = __find_and_get_object(ptr, alias);
> +	if (!object &&
> +	    !prio_tree_empty(&alias_tree_root))
> +		object = __find_and_get_alias(ptr, alias);
> +
>  	rcu_read_unlock();
>  
>  	return object;
> @@ -524,6 +608,7 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
>  	object->count = 0;			/* white color initially */
>  	object->jiffies = jiffies;
>  	object->checksum = 0;
> +	object->alias = NULL;
>  
>  	/* task information */
>  	if (in_irq()) {
> @@ -547,7 +632,7 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
>  	object->trace_len = __save_stack_trace(object->trace);
>  
>  	INIT_PRIO_TREE_NODE(&object->tree_node);
> -	object->tree_node.start = ptr;
> +	to_address(object) = ptr;
>  	object->tree_node.last = ptr + size - 1;
>  
>  	write_lock_irqsave(&kmemleak_lock, flags);
> @@ -577,6 +662,57 @@ out:
>  	return object;
>  }
>  
> +static void create_alias_object(struct kmemleak_object *object,
> +				unsigned long ptr)
> +{
> +	struct kmemleak_alias *alias;
> +	struct prio_tree_node *node;
> +	unsigned long flags;
> +
> +	alias = kmem_cache_alloc(alias_cache, GFP_KERNEL);
> +	if (!alias) {
> +		kmemleak_stop("Cannot allocate a kmemleak_alias structure\n");
> +		return;
> +	}
> +	INIT_LIST_HEAD(&alias->alias_list);
> +	INIT_PRIO_TREE_NODE(&alias->tree_node);
> +	to_address(alias) = ptr;
> +
> +	spin_lock_irqsave(&object->lock, flags);
> +	alias->tree_node.last = ptr + object->size - 1;
> +	alias->object = object;
> +	object->alias = alias;
> +	spin_unlock_irqrestore(&object->lock, flags);
> +
> +	write_lock_irqsave(&kmemleak_lock, flags);
> +
> +	node = prio_tree_insert(&alias_tree_root, &alias->tree_node);
> +	if (!node) {
> +		kmemleak_warn("Cannot allocate a kmemleak_alias structure\n");
> +		kmem_cache_free(alias_cache, alias);
> +	}
> +	list_add_tail_rcu(&alias->alias_list, &alias_list);
> +
> +	write_unlock_irqrestore(&kmemleak_lock, flags);
> +}
> +
> +static void __delete_alias_object(struct kmemleak_object *object)
> +{
> +	prio_tree_remove(&alias_tree_root, &object->alias->tree_node);
> +	list_del_rcu(&object->alias->alias_list);
> +	kmem_cache_free(alias_cache, object->alias);
> +	object->alias = NULL;
> +}
> +
> +static void delete_alias_object(struct kmemleak_object *object)
> +{
> +	unsigned long flags;
> +
> +	write_lock_irqsave(&kmemleak_lock, flags);
> +	__delete_alias_object(object);
> +	write_unlock_irqrestore(&kmemleak_lock, flags);
> +}
> +
>  /*
>   * Remove the metadata (struct kmemleak_object) for a memory block from the
>   * object_list and object_tree_root and decrement its use_count.
> @@ -588,6 +724,8 @@ static void __delete_object(struct kmemleak_object *object)
>  	write_lock_irqsave(&kmemleak_lock, flags);
>  	prio_tree_remove(&object_tree_root, &object->tree_node);
>  	list_del_rcu(&object->object_list);
> +	if (object->alias)
> +		__delete_alias_object(object);
>  	write_unlock_irqrestore(&kmemleak_lock, flags);
>  
>  	WARN_ON(!(object->flags & OBJECT_ALLOCATED));
> @@ -630,7 +768,7 @@ static void delete_object_full(unsigned long ptr)
>   */
>  static void delete_object_part(unsigned long ptr, size_t size)
>  {
> -	struct kmemleak_object *object;
> +	struct kmemleak_object *object, *new;
>  	unsigned long start, end;
>  
>  	object = find_and_get_object(ptr, 1);
> @@ -652,12 +790,24 @@ static void delete_object_part(unsigned long ptr, size_t size)
>  	 */
>  	start = object->pointer;
>  	end = object->pointer + object->size;
> -	if (ptr > start)
> -		create_object(start, ptr - start, object->min_count,
> -			      GFP_KERNEL);
> -	if (ptr + size < end)
> -		create_object(ptr + size, end - ptr - size, object->min_count,
> -			      GFP_KERNEL);
> +	if (ptr > start) {
> +		new = create_object(start, ptr - start, object->min_count,
> +				    GFP_KERNEL);
> +		if (new && unlikely(object->alias))
> +			create_alias_object(new, to_address(object->alias));
> +	}
> +	if (ptr + size < end) {
> +		new = create_object(ptr + size, end - ptr - size,
> +				    object->min_count, GFP_KERNEL);
> +		if (new && unlikely(object->alias)) {
> +			unsigned long alias_ptr;
> +
> +			alias_ptr = to_address(object->alias);
> +			alias_ptr += ptr - start + size;
> +
> +			create_alias_object(new, alias_ptr);
> +		}
> +	}
>  
>  	put_object(object);
>  }
> @@ -944,6 +1094,38 @@ void __ref kmemleak_no_scan(const void *ptr)
>  }
>  EXPORT_SYMBOL(kmemleak_no_scan);
>  
> +void kmemleak_add_alias(const void *ptr, const void *alias)
> +{
> +	struct kmemleak_object *object;
> +
> +	pr_debug("%s(0x%p -> 0x%p)\n", __func__, ptr, alias);
> +
> +	object = find_and_get_object((unsigned long)ptr, 0);
> +	if (!object) {
> +		kmemleak_warn("Aliasing unknown object at 0x%p\n", ptr);
> +		return;
> +	}
> +	create_alias_object(object, (unsigned long)alias);
> +	put_object(object);
> +}
> +EXPORT_SYMBOL(kmemleak_add_alias);
> +
> +void kmemleak_unalias(const void *alias)
> +{
> +	struct kmemleak_object *object;
> +
> +	pr_debug("%s(0x%p)\n", __func__, alias);
> +
> +	object = find_and_get_alias((unsigned long)alias, 0);
> +	if (!object) {
> +		kmemleak_warn("Aliasing unknown object at 0x%p\n", alias);
> +		return;
> +	}
> +	delete_alias_object(object);
> +	put_object(object);
> +}
> +EXPORT_SYMBOL(kmemleak_unalias);
> +
>  /*
>   * Update an object's checksum and return true if it was modified.
>   */
> @@ -1007,7 +1189,7 @@ static void scan_block(void *_start, void *_end,
>  
>  		pointer = *ptr;
>  
> -		object = find_and_get_object(pointer, 1);
> +		object = find_and_get_object_with_alias(pointer, 1);
>  		if (!object)
>  			continue;
>  		if (object == scanned) {
> @@ -1620,8 +1802,10 @@ void __init kmemleak_init(void)
>  	jiffies_scan_wait = msecs_to_jiffies(SECS_SCAN_WAIT * 1000);
>  
>  	object_cache = KMEM_CACHE(kmemleak_object, SLAB_NOLEAKTRACE);
> +	alias_cache = KMEM_CACHE(kmemleak_alias, SLAB_NOLEAKTRACE);
>  	scan_area_cache = KMEM_CACHE(kmemleak_scan_area, SLAB_NOLEAKTRACE);
>  	INIT_PRIO_TREE_ROOT(&object_tree_root);
> +	INIT_PRIO_TREE_ROOT(&alias_tree_root);
>  
>  	/* the kernel is still in UP mode, so disabling the IRQs is enough */
>  	local_irq_save(flags);
> -- 
> 1.7.1.rc2
> 
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