[PATCH v2 03/10] zram: use zram->lock to protect zram_free_page() in swap free notify path

From: Jiang Liu
Date: Tue Jun 04 2013 - 12:11:13 EST

zram_free_page() is protected by down_write(&zram->lock) when called by
zram_bvec_write(), but there's no such protection when called by
zram_slot_free_notify(), which may cause wrong states to zram object.

There are two possible consequences of this issue:
1) It may cause invalid memory access if we read from a zram device used
as swap device. (Not sure whether it's legal to make read/write
requests to a zram device used as swap device.)
2) It may cause some fields (bad_compress, good_compress, pages_stored)
in zram->stats wrong if the swap layer makes concurrently call to

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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
drivers/staging/zram/zram_drv.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 5a2f20b..847d207 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -582,7 +582,9 @@ static void zram_slot_free_notify(struct block_device *bdev,
struct zram *zram;

zram = bdev->bd_disk->private_data;
+ down_write(&zram->lock);
zram_free_page(zram, index);
+ up_write(&zram->lock);
zram_stat64_inc(zram, &zram->stats.notify_free);


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