linux-kernel - Re: [PATCH v2] kasan: avoid overflowing quarantine size on low memory systems

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Message-Id: <20160810155015.bffc044a171466b2fdf5195e@linux-foundation.org>
Date:	Wed, 10 Aug 2016 15:50:15 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alexander Potapenko <glider@...gle.com>
Cc:	dvyukov@...gle.com, kcc@...gle.com, aryabinin@...tuozzo.com,
	adech.fo@...il.com, cl@...ux.com, rostedt@...dmis.org,
	js1304@...il.com, iamjoonsoo.kim@....com, kuthonuzo.luruo@....com,
	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v2] kasan: avoid overflowing quarantine size on low
 memory systems

On Tue,  2 Aug 2016 12:27:00 +0200 Alexander Potapenko <glider@...gle.com> wrote:

> If the total amount of memory assigned to quarantine is less than the
> amount of memory assigned to per-cpu quarantines, |new_quarantine_size|
> may overflow. Instead, set it to zero.
> 
> ...
>
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -196,7 +196,7 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
>  
>  void quarantine_reduce(void)
>  {
> -	size_t new_quarantine_size;
> +	size_t new_quarantine_size, percpu_quarantines;
>  	unsigned long flags;
>  	struct qlist_head to_free = QLIST_INIT;
>  	size_t size_to_free = 0;
> @@ -214,7 +214,9 @@ void quarantine_reduce(void)
>  	 */
>  	new_quarantine_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
>  		QUARANTINE_FRACTION;
> -	new_quarantine_size -= QUARANTINE_PERCPU_SIZE * num_online_cpus();
> +	percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
> +	new_quarantine_size = (new_quarantine_size < percpu_quarantines) ?
> +		0 : new_quarantine_size - percpu_quarantines;
>  	WRITE_ONCE(quarantine_size, new_quarantine_size);
>  
>  	last = global_quarantine.head;

Confused.  Which kernel version is this supposed to apply to?