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Subject[002/289] block: Fix race during disk initialization
2.6.36-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Jan Kara <jack@suse.cz>

commit 01ea50638bc04ca5259f5711fcdedefcdde1cf43 upstream.

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

Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
block/genhd.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- 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);



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