blockdev: Avoid two active bdev inodes for one device (560e7cb2) · Commits · 戴 / test

When blkdev_open() races with device removal and creation it can happen that unhashed bdev inode gets associated with newly created gendisk like: CPU0 CPU1 blkdev_open() bdev = bd_acquire() del_gendisk() bdev_unhash_inode(bdev); remove device create new device with the same number __blkdev_get() disk = get_gendisk() - gets reference to gendisk of the new device Now another blkdev_open() will not find original 'bdev' as it got unhashed, create a new one and associate it with the same 'disk' at which point problems start as we have two independent page caches for one device. Fix the problem by verifying that the bdev inode didn't get unhashed before we acquired gendisk reference. That way we make sure gendisk can get associated only with visible bdev inodes. Tested-by:

Hou Tao <houtao1@huawei.com> Signed-off-by:

Jan Kara <jack@suse.cz> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

fs/block_dev.c

+23 −2

Original line number	Diff line number	Diff line
		@@ -1058,6 +1058,27 @@ retry:
		return 0;
		}

		static struct gendisk bdev_get_gendisk(struct block_device bdev, int *partno)
		{
		struct gendisk *disk = get_gendisk(bdev->bd_dev, partno);

		if (!disk)
		return NULL;
		/*
		* Now that we hold gendisk reference we make sure bdev we looked up is
		* not stale. If it is, it means device got removed and created before
		* we looked up gendisk and we fail open in such case. Associating
		* unhashed bdev with newly created gendisk could lead to two bdevs
		* (and thus two independent caches) being associated with one device
		* which is bad.
		*/
		if (inode_unhashed(bdev->bd_inode)) {
		put_disk_and_module(disk);
		return NULL;
		}
		return disk;
		}

		/**
		* bd_start_claiming - start claiming a block device
		* @bdev: block device of interest
		@@ -1094,7 +1115,7 @@ static struct block_device bd_start_claiming(struct block_device bdev,
		* @bdev might not have been initialized properly yet, look up
		* and grab the outer block device the hard way.
		*/
		disk = get_gendisk(bdev->bd_dev, &partno);
		disk = bdev_get_gendisk(bdev, &partno);
		if (!disk)
		return ERR_PTR(-ENXIO);

		@@ -1429,7 +1450,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
		restart:

		ret = -ENXIO;
		disk = get_gendisk(bdev->bd_dev, &partno);
		disk = bdev_get_gendisk(bdev, &partno);
		if (!disk)
		goto out;

Admin message