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

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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>
This commit is contained in:
Jiang Liu 2013-06-07 00:07:23 +08:00 committed by Greg Kroah-Hartman
parent 6030ea9b35
commit 57ab048532
2 changed files with 5 additions and 2 deletions
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2
drivers/staging/zram/zram_drv.c
View File

@ -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);
}

5
drivers/staging/zram/zram_drv.h
View File

@ -93,8 +93,9 @@ struct zram_meta {
struct zram {
struct zram_meta *meta;
spinlock_t stat64_lock; /* protect 64-bit stats */
struct rw_semaphore lock; /* protect compression buffers and table
* against concurrent read and writes */
struct rw_semaphore lock; /* protect compression buffers, table,
* 32bit stat counters against concurrent
* notifications, reads and writes */
struct request_queue *queue;
struct gendisk *disk;
int init_done;