From: Jiang Liu <liuj97@gmail.com>
Date: Thu, 6 Jun 2013 16:07:23 +0000 (+0800)
Subject: zram: use zram->lock to protect zram_free_page() in swap free notify path
X-Git-Tag: omap-for-v3.11/fixes-for-merge-window~76^2~229
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=57ab048532c0d975538cebd4456491b5c34248f4;p=pandora-kernel.git

zram: use zram->lock to protect zram_free_page() in swap free notify path

zram_slot_free_notify() is free-running without any protection from
concurrent operations. So there are race conditions between
zram_bvec_read()/zram_bvec_write() and zram_slot_free_notify(),
and possible consequences include:
1) Trigger BUG_ON(!handle) on zram_bvec_write() side.
2) Access to freed pages on zram_bvec_read() side.
3) Break some fields (bad_compress, good_compress, pages_stored)
   in zram->stats if the swap layer makes concurrently call to
   zram_slot_free_notify().

So enhance zram_slot_free_notify() to acquire writer lock on zram->lock
before calling zram_free_page().

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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