[PATCH 6.12.y 2/3] zram: use zram_read_from_zspool() in writeback

[Sasha Levin <sashal@kernel.org>]

From: Sergey Senozhatsky <senozhatsky@chromium.org>

[ Upstream commit b8d3ff7bb5111c6a88d5672469de445d9b46cf22 ]

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.

Link: https://lkml.kernel.org/r/20241218063513.297475-7-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 894913e2d35c ("zram: fix out-of-bounds access in writeback_store()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/block/zram/zram_drv.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index afd1eb7a8fffb..28b4ce88cf145 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)
 {
@@ -694,14 +694,12 @@ static ssize_t writeback_store(struct device *dev,
 		zram_set_flag(zram, index, ZRAM_UNDER_WB);
 		/* Need for hugepage writeback racing */
 		zram_set_flag(zram, index, ZRAM_IDLE);
-		zram_slot_unlock(zram, index);
-		if (zram_read_page(zram, page, index, NULL)) {
-			zram_slot_lock(zram, index);
+		if (zram_read_from_zspool(zram, page, index)) {
 			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
 			zram_clear_flag(zram, index, ZRAM_IDLE);
-			zram_slot_unlock(zram, index);
-			continue;
+			goto next;
 		}
+		zram_slot_unlock(zram, index);
 
 		bio_init(&bio, zram->bdev, &bio_vec, 1,
 			 REQ_OP_WRITE | REQ_SYNC);
-- 
2.53.0