Re: [PATCH RESEND 1/2] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrentâly

From: Minchan Kim
Date: Fri Oct 25 2013 - 06:15:42 EST

On Thu, Oct 24, 2013 at 05:51:11PM +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@xxxxxxxxxxx>
> Reviewed-by: Bob Liu <bob.liu@xxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Acked-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx>

Thanks, Weijie!

Kind regards,
Minchan Kim
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