[PATCH RESEND] mtd:spi-nor: Fix an issue of releasing resources during read/write

[Yicong Yang]

From: Xiang Chen <chenxiang66 at hisilicon.com>

If rmmod the driver during read or write, the driver will release the
resources which are used during read or write, so it is possible to
refer to NULL pointer.

Use the testcase "mtd_debug read /dev/mtd0 0xc00000 0x400000 dest_file &
sleep 0.5;rmmod spi_hisi_sfc_v3xx.ko", the issue can be reproduced in
hisi_sfc_v3xx driver.

To avoid the issue, fill the interface _get_device and _put_device of
mtd_info to grab the reference to the spi controller driver module, so
the request of rmmod the driver is rejected before read/write is finished.

Signed-off-by: Xiang Chen <chenxiang66 at hisilicon.com>
Signed-off-by: Yicong Yang <yangyicong at hisilicon.com>
---
 drivers/mtd/spi-nor/core.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 0522304..72bc134 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -3301,6 +3301,37 @@ static void spi_nor_resume(struct mtd_info *mtd)
 		dev_err(dev, "resume() failed\n");
 }
 
+static int spi_nor_get_device(struct mtd_info *mtd)
+{
+	struct mtd_info *master = mtd_get_master(mtd);
+	struct spi_nor *nor = mtd_to_spi_nor(master);
+	struct device *dev;
+
+	if (nor->spimem)
+		dev = nor->spimem->spi->controller->dev.parent;
+	else
+		dev = nor->dev;
+
+	if (!try_module_get(dev->driver->owner))
+		return -ENODEV;
+
+	return 0;
+}
+
+static void spi_nor_put_device(struct mtd_info *mtd)
+{
+	struct mtd_info *master = mtd_get_master(mtd);
+	struct spi_nor *nor = mtd_to_spi_nor(master);
+	struct device *dev;
+
+	if (nor->spimem)
+		dev = nor->spimem->spi->controller->dev.parent;
+	else
+		dev = nor->dev;
+
+	module_put(dev->driver->owner);
+}
+
 void spi_nor_restore(struct spi_nor *nor)
 {
 	/* restore the addressing mode */
@@ -3495,6 +3526,8 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 	mtd->_read = spi_nor_read;
 	mtd->_suspend = spi_nor_suspend;
 	mtd->_resume = spi_nor_resume;
+	mtd->_get_device = spi_nor_get_device;
+	mtd->_put_device = spi_nor_put_device;
 
 	if (nor->params->locking_ops) {
 		mtd->_lock = spi_nor_lock;
-- 
2.8.1