[PATCH 1/2] zram: use zram_read_from_zspool() in writeback

[Sergey Senozhatsky]

We only can read pages from zspool in writeback, zram_read_page()
is not really right in that context not only because it's a more
generic function that handles ZRAM_WB pages, but also because it
requires us to unlock slot between slot flag check and actual page
read.  Use zram_read_from_zspool() instead and do slot flags check
and page read under the same slot lock.

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---

This is not -stable material.  The patch simply makes things look
more logical and corect.  The page content still can change while
we are in submit_bio_wait() and we try to handle that when
submit_bio_wait() returns.

 drivers/block/zram/zram_drv.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index d06761ad541f..0a924fae02a4 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -55,8 +55,8 @@ static size_t huge_class_size;
 static const struct block_device_operations zram_devops;
 
 static void zram_free_page(struct zram *zram, size_t index);
-static int zram_read_page(struct zram *zram, struct page *page, u32 index,
-			  struct bio *parent);
+static int zram_read_from_zspool(struct zram *zram, struct page *page,
+				 u32 index);
 
 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
@@ -831,13 +831,10 @@ static ssize_t writeback_store(struct device *dev,
 		 */
 		if (!zram_test_flag(zram, index, ZRAM_PP_SLOT))
 			goto next;
+		if (zram_read_from_zspool(zram, page, index))
+			goto next;
 		zram_slot_unlock(zram, index);
 
-		if (zram_read_page(zram, page, index, NULL)) {
-			release_pp_slot(zram, pps);
-			continue;
-		}
-
 		bio_init(&bio, zram->bdev, &bio_vec, 1,
 			 REQ_OP_WRITE | REQ_SYNC);
 		bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
-- 
2.47.1.613.gc27f4b7a9f-goog