[BLOCK] Fix oops on removal of SD/MMC card

The block layer keeps a reference (driverfs_dev) to the struct
device associated with the block device, and uses it internally
for generating uevents in block_uevent.

Block device uevents include umounting the partition, which can
occur after the backing device has been removed.

Unfortunately, this reference is not counted.  This means that
if the struct device is removed from the device tree, the block
layers reference will become stale.

Guard against this by holding a reference to the struct device
in add_disk(), and only drop the reference when we're releasing
the gendisk kobject - in other words when we can be sure that no
further uevents will be generated for this block device.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Jens Axboe <axboe@suse.de>

diff --git a/block/genhd.c b/block/genhd.c
index 5a8d3bf02f1715702fe94515339f1cdfbfd3d088..d96572589621e10ecae8107616459f227e3be111 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -182,6 +182,7 @@ static int exact_lock(dev_t dev, void *data)
  */
 void add_disk(struct gendisk *disk)
 {
+       get_device(disk->driverfs_dev);
        disk->flags |= GENHD_FL_UP;
        blk_register_region(MKDEV(disk->major, disk->first_minor),
                            disk->minors, NULL, exact_match, exact_lock, disk);
@@ -427,6 +428,7 @@ static struct attribute * default_attrs[] = {
 static void disk_release(struct kobject * kobj)
 {
        struct gendisk *disk = to_disk(kobj);
+       put_device(disk->driverfs_dev);
        kfree(disk->random);
        kfree(disk->part);
        free_disk_stats(disk);