Read slot's block id under slot-lock.  We release the
slot-lock for bdev read so, technically, slot still can
get freed in the meantime, but at least we will read
bdev block (page) that holds previous know slot data,
not from slot->handle bdev block, which can be anything
at that point.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 93365811781b..77d0e636e053 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1980,14 +1980,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 		ret = zram_read_from_zspool(zram, page, index);
 		zram_slot_unlock(zram, index);
 	} else {
+		unsigned long blk_idx = zram_get_handle(zram, index);
+
 		/*
 		 * The slot should be unlocked before reading from the backing
 		 * device.
 		 */
 		zram_slot_unlock(zram, index);
-
-		ret = read_from_bdev(zram, page, zram_get_handle(zram, index),
-				     parent);
+		ret = read_from_bdev(zram, page, blk_idx, parent);
 	}
 
 	/* Should NEVER happen. Return bio error if it does. */
-- 
2.52.0.rc1.455.g30608eb744-goog