linux-kernel - Re: [PATCH v2 2/4] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently

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Date:	Mon, 9 Sep 2013 11:28:15 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Weijie Yang <weijie.yang@...sung.com>
Cc:	minchan@...nel.org, bob.liu@...cle.com, weijie.yang.kh@...il.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] mm/zswap: bugfix: memory leak when invalidate and
 reclaim occur concurrently

On Fri, Sep 06, 2013 at 01:16:45PM +0800, Weijie Yang wrote:
> Consider the following scenario:
> thread 0: reclaim entry x (get refcount, but not call zswap_get_swap_cache_page)
> thread 1: call zswap_frontswap_invalidate_page to invalidate entry x.
> 	finished, entry x and its zbud is not freed as its refcount != 0
> 	now, the swap_map[x] = 0
> thread 0: now call zswap_get_swap_cache_page
> 	swapcache_prepare return -ENOENT because entry x is not used any more
> 	zswap_get_swap_cache_page return ZSWAP_SWAPCACHE_NOMEM
> 	zswap_writeback_entry do nothing except put refcount
> Now, the memory of zswap_entry x and its zpage leak.
> 
> Modify:
> - check the refcount in fail path, free memory if it is not referenced.
> - use ZSWAP_SWAPCACHE_FAIL instead of ZSWAP_SWAPCACHE_NOMEM as the fail path
> can be not only caused by nomem but also by invalidate.
> 
> Signed-off-by: Weijie Yang <weijie.yang@...sung.com>

Thanks!

Acked-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>

Seth

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