mtd: fix bdev exclusive open bugs in block2mtd::add_device()

There are two bdev exclusive open bugs.

* open_bdev_exclusive() must not be called with NULL holder.  Use dev
  as the holder.

* open_by_devnum() doesn't open the bdev exclusively but
  block2mtd_free_device() always assumes it.  Explicitly claim the
  bdev.

The latter is rather clumsy but will be simplified with future
blkdev_get/put() cleanups.

- Updated to use local variable @mode to cache FMODE_* masks as
  suggested by Artem Bityutskiy.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: linux-mtd@lists.infradead.org
Cc: Artem Bityutskiy <dedekind1@gmail.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/drivers/mtd/devices/block2mtd.c b/drivers/mtd/devices/block2mtd.c
index 2cf0cc6a4189..a9e2d3b38aeb 100644
--- a/drivers/mtd/devices/block2mtd.c
+++ b/drivers/mtd/devices/block2mtd.c
@@ -234,6 +234,7 @@ static void block2mtd_free_device(struct block2mtd_dev *dev)
 /* FIXME: ensure that mtd->size % erase_size == 0 */
 static struct block2mtd_dev *add_device(char *devname, int erase_size)
 {
+        const fmode_t mode = FMODE_READ | FMODE_WRITE;
         struct block_device *bdev;
         struct block2mtd_dev *dev;
         char *name;
@@ -246,7 +247,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size)
                 return NULL;
 
         /* Get a handle on the device */
-        bdev = open_bdev_exclusive(devname, FMODE_READ|FMODE_WRITE, NULL);
+        bdev = open_bdev_exclusive(devname, mode, dev);
 #ifndef MODULE
         if (IS_ERR(bdev)) {
 
@@ -255,7 +256,15 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size)
 
                 dev_t devt = name_to_dev_t(devname);
                 if (devt) {
-                        bdev = open_by_devnum(devt, FMODE_WRITE | FMODE_READ);
+                        bdev = open_by_devnum(devt, mode);
+                        if (!IS_ERR(bdev)) {
+                                int ret;
+                                ret = bd_claim(bdev, dev);
+                                if (ret) {
+                                        blkdev_put(bdev, mode);
+                                        bdev = ERR_PTR(ret);
+                                }
+                        }
                 }
         }
 #endif