linux-kernel - [PATCH] [2/223] block: Fix race during disk initialization

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Date:	Mon, 13 Dec 2010 00:44:56 +0100 (CET)
From:	Andi Kleen <andi@...stfloor.org>
To:	jack@...e.cz, jaxboe@...ionio.com, gregkh@...e.de,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org, stable@...nel.org
Subject: [PATCH] [2/223] block: Fix race during disk initialization

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Jan Kara <jack@...e.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@...inger.net>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

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

Index: linux/block/genhd.c
===================================================================
--- linux.orig/block/genhd.c
+++ linux/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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