Re: [STABLE PATCH] slub: make ->cpu_partial unsigned int

[Matthew Wilcox]

On Sun, Sep 30, 2018 at 06:28:21PM +0800, zhong jiang wrote:
> From: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> 
> [ Upstream commit e5d9998f3e09359b372a037a6ac55ba235d95d57 ]
> 
>         /*
>          * cpu_partial determined the maximum number of objects
>          * kept in the per cpu partial lists of a processor.
>          */
> 
> Can't be negative.
> 
> I hit a real issue that it will result in a large number of memory leak.
> Becuase Freeing slabs are in interrupt context. So it can trigger this issue.
> put_cpu_partial can be interrupted more than once.
> due to a union struct of lru and pobjects in struct page, when other core handles
> page->lru list, for eaxmple, remove_partial in freeing slab code flow, It will
> result in pobjects being a negative value(0xdead0000). Therefore, a large number
> of slabs will be added to per_cpu partial list.
> 
> I had posted the issue to community before. The detailed issue description is as follows.
> 
> https://www.spinics.net/lists/kernel/msg2870979.html
> 
> After applying the patch, The issue is fixed. So the patch is a effective bugfix.
> It should go into stable.
> 
> Link: http://lkml.kernel.org/r/20180305200730.15812-15-adobriyan@xxxxxxxxx
> Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> Acked-by: Christoph Lameter <cl@xxxxxxxxx>

Hang on.  Christoph acked the _original_ patch going into upstream.
When he reviewed this patch for _stable_ last week, he asked for more
investigation.  Including this patch in stable is misleading.

> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.4.x
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx>
> ---
>  include/linux/slub_def.h | 3 ++-
>  mm/slub.c                | 6 +++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index 3388511..9b681f2 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -67,7 +67,8 @@ struct kmem_cache {
>  	int size;		/* The size of an object including meta data */
>  	int object_size;	/* The size of an object without meta data */
>  	int offset;		/* Free pointer offset. */
> -	int cpu_partial;	/* Number of per cpu partial objects to keep around */
> +	/* Number of per cpu partial objects to keep around */
> +	unsigned int cpu_partial;
>  	struct kmem_cache_order_objects oo;
>  
>  	/* Allocation and freeing of slabs */
> diff --git a/mm/slub.c b/mm/slub.c
> index 2284c43..c33b0e1 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1661,7 +1661,7 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
>  {
>  	struct page *page, *page2;
>  	void *object = NULL;
> -	int available = 0;
> +	unsigned int available = 0;
>  	int objects;
>  
>  	/*
> @@ -4674,10 +4674,10 @@ static ssize_t cpu_partial_show(struct kmem_cache *s, char *buf)
>  static ssize_t cpu_partial_store(struct kmem_cache *s, const char *buf,
>  				 size_t length)
>  {
> -	unsigned long objects;
> +	unsigned int objects;
>  	int err;
>  
> -	err = kstrtoul(buf, 10, &objects);
> +	err = kstrtouint(buf, 10, &objects);
>  	if (err)
>  		return err;
>  	if (objects && !kmem_cache_has_cpu_partial(s))
> -- 
> 1.7.12.4
>