mtd: Fix issue where write_cached_data() fails but write() still retu…

…rns success

The following sequence is problematic:

mtdblock_flush()
    -->write_cached_data()
        --->erase_write()
        mtdblock: erase of region [0x40000, 0x20000] on "xxx" failed

Problem is: mtdblock_flush() always returns 0. Indeed, even if
write_cached_data() fails and data is not written to the device,
syscall_write() still returns success. Avoid this situation by
actually returning the error coming out of write_cached_data().

Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1584674111-101462-1-git-send-email-nixiaoming@huawei.com

drivers/mtd/mtdblock.c

@@ -294,12 +294,13 @@ static void mtdblock_release(struct mtd_blktrans_dev *mbd)
 static int mtdblock_flush(struct mtd_blktrans_dev *dev)
 {
 	struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
+	int ret;
 
 	mutex_lock(&mtdblk->cache_mutex);
-	write_cached_data(mtdblk);
+	ret = write_cached_data(mtdblk);
 	mutex_unlock(&mtdblk->cache_mutex);
 	mtd_sync(dev->mtd);
-	return 0;
+	return ret;
 }
 
 static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)