Commit 94007751 authored Sep 10, 2011 by NeilBrown

Avoid dereferencing a 'request_queue' after last close.



On the last close of an 'md' device which as been stopped, the device
is destroyed and in particular the request_queue is freed.  The free
is done in a separate thread so it might happen a short time later.

__blkdev_put calls bdev_inode_switch_bdi *after* ->release has been
called.

Since commit f758eeab
bdev_inode_switch_bdi will dereference the 'old' bdi, which lives
inside a request_queue, to get a spin lock.  This causes the last
close on an md device to sometime take a spin_lock which lives in
freed memory - which results in an oops.

So move the called to bdev_inode_switch_bdi before the call to
->release.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Acked-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: stable@kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>

parent 43220aa0

fs/block_dev.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -1429,6 +1429,11 @@ static int __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
		WARN_ON_ONCE(bdev->bd_holders);
		sync_blockdev(bdev);
		kill_bdev(bdev);
		/* ->release can cause the old bdi to disappear,
		* so must switch it out first
		*/
		bdev_inode_switch_bdi(bdev->bd_inode,
		&default_backing_dev_info);
		}
		if (bdev->bd_contains == bdev) {
		if (disk->fops->release)
		@@ -1442,8 +1447,6 @@ static int __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
		disk_put_part(bdev->bd_part);
		bdev->bd_part = NULL;
		bdev->bd_disk = NULL;
		bdev_inode_switch_bdi(bdev->bd_inode,
		&default_backing_dev_info);
		if (bdev != bdev->bd_contains)
		victim = bdev->bd_contains;
		bdev->bd_contains = NULL;