block: Fix race during disk initialization

When a new disk is being discovered, add_disk() first ties the bdev to gendisk
(via register_disk()->blkdev_get()) and only after that calls
bdi_register_bdev(). Because register_disk() also creates disk's kobject, it
can happen that userspace manages to open and modify the device's data (or
inode) before its BDI is properly initialized leading to a warning in
__mark_inode_dirty().

Fix the problem by registering BDI early enough.

This patch addresses https://bugzilla.kernel.org/show_bug.cgi?id=16312

Cc: stable@kernel.org
Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 5c9c503de423..7923e720ddf5 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -541,13 +541,15 @@ void add_disk(struct gendisk *disk)
         disk->major = MAJOR(devt);
         disk->first_minor = MINOR(devt);
 
+        /* Register BDI before referencing it from bdev */ 
+        bdi = &disk->queue->backing_dev_info;
+        bdi_register_dev(bdi, disk_devt(disk));
+
         blk_register_region(disk_devt(disk), disk->minors, NULL,
                             exact_match, exact_lock, disk);
         register_disk(disk);
         blk_register_queue(disk);
 
-        bdi = &disk->queue->backing_dev_info;
-        bdi_register_dev(bdi, disk_devt(disk));
         retval = sysfs_create_link(&disk_to_dev(disk)->kobj, &bdi->dev->kobj,
                                    "bdi");
         WARN_ON(retval);