linux-kernel - Re: [PATCH 6/6] mm/zpool: prevent zbud/zsmalloc from unloading when used

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Date:	Tue, 27 May 2014 17:40:02 -0500
From:	Seth Jennings <sjennings@...iantweb.net>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Minchan Kim <minchan@...nel.org>,
	Weijie Yang <weijie.yang@...sung.com>,
	Nitin Gupta <ngupta@...are.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bob Liu <bob.liu@...cle.com>, Hugh Dickins <hughd@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] mm/zpool: prevent zbud/zsmalloc from unloading when
 used

On Sat, May 24, 2014 at 03:06:09PM -0400, Dan Streetman wrote:
> Add try_module_get() to pool creation functions for zbud and zsmalloc,
> and module_put() to pool destruction functions, since they now can be
> modules used via zpool.  Without usage counting, they could be unloaded
> while pool(s) were active, resulting in an oops.

I like the idea here, but what about doing this in the zpool layer? For
me, it is kinda weird for a module to be taking a ref on itself.  Maybe
this is excepted practice.  Is there precedent for this?

What about having the zbud/zsmalloc drivers pass their module pointers
to zpool_register_driver() as an additional field in struct zpool_driver
and have zpool take the reference?  Since zpool is the one in trouble if
the driver is unloaded.

Seth

> 
> Signed-off-by: Dan Streetman <ddstreet@...e.org>
> Cc: Seth Jennings <sjennings@...iantweb.net>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Nitin Gupta <ngupta@...are.org>
> Cc: Weijie Yang <weijie.yang@...sung.com>
> ---
> 
> New for this patch set.
> 
>  mm/zbud.c     | 5 +++++
>  mm/zsmalloc.c | 5 +++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/mm/zbud.c b/mm/zbud.c
> index 8a72cb1..2b3689c 100644
> --- a/mm/zbud.c
> +++ b/mm/zbud.c
> @@ -282,6 +282,10 @@ struct zbud_pool *zbud_create_pool(gfp_t gfp, struct zbud_ops *ops)
>  	pool = kmalloc(sizeof(struct zbud_pool), GFP_KERNEL);
>  	if (!pool)
>  		return NULL;
> +	if (!try_module_get(THIS_MODULE)) {
> +		kfree(pool);
> +		return NULL;
> +	}
>  	spin_lock_init(&pool->lock);
>  	for_each_unbuddied_list(i, 0)
>  		INIT_LIST_HEAD(&pool->unbuddied[i]);
> @@ -302,6 +306,7 @@ struct zbud_pool *zbud_create_pool(gfp_t gfp, struct zbud_ops *ops)
>  void zbud_destroy_pool(struct zbud_pool *pool)
>  {
>  	kfree(pool);
> +	module_put(THIS_MODULE);
>  }
>  
>  /**
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 07c3130..2cc2647 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -946,6 +946,10 @@ struct zs_pool *zs_create_pool(gfp_t flags)
>  	pool = kzalloc(ovhd_size, GFP_KERNEL);
>  	if (!pool)
>  		return NULL;
> +	if (!try_module_get(THIS_MODULE)) {
> +		kfree(pool);
> +		return NULL;
> +	}
>  
>  	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
>  		int size;
> @@ -985,6 +989,7 @@ void zs_destroy_pool(struct zs_pool *pool)
>  		}
>  	}
>  	kfree(pool);
> +	module_put(THIS_MODULE);
>  }
>  EXPORT_SYMBOL_GPL(zs_destroy_pool);
>  
> -- 
> 1.8.3.1
> 
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