diff options
| author | Jiang Liu <liuj97@gmail.com> | 2013-06-07 00:07:23 +0800 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2013-07-27 05:34:07 +0100 |
| commit | 9e443904906ca2b5b3ae71f34ac4a4fa6905623e (patch) | |
| tree | 026657122c99b02939c22d720e2632aedc821a7c | |
| parent | fd162a76f16083157e32fe5f488f39a319b93fad (diff) | |
| download | lwn-9e443904906ca2b5b3ae71f34ac4a4fa6905623e.tar.gz lwn-9e443904906ca2b5b3ae71f34ac4a4fa6905623e.zip | |
zram: use zram->lock to protect zram_free_page() in swap free notify path
commit 57ab048532c0d975538cebd4456491b5c34248f4 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | drivers/staging/zram/zram_drv.c | 2 | ||||
| -rw-r--r-- | drivers/staging/zram/zram_drv.h | 5 |
2 files changed, 5 insertions, 2 deletions
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c index e87af2914ddc..785a94750993 100644 --- a/drivers/staging/zram/zram_drv.c +++ b/drivers/staging/zram/zram_drv.c @@ -702,7 +702,9 @@ 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); } diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h index e5cd2469b6a0..87f2fec1bc94 100644 --- a/drivers/staging/zram/zram_drv.h +++ b/drivers/staging/zram/zram_drv.h @@ -107,8 +107,9 @@ struct zram { void *compress_buffer; struct table *table; 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; |