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    Subject[PATCH 4.8 32/85] btrfs: clean the old superblocks before freeing the device
    Date
    4.8-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jeff Mahoney <jeffm@suse.com>

    commit cea67ab92d3d4da9f2b4141d87cb8664757daca0 upstream.

    btrfs_rm_device frees the block device but then re-opens it using
    the saved device name. A race exists between the close and the
    re-open that allows the block size to be changed. The result
    is getting stuck forever in the reclaim loop in __getblk_slow.

    This patch moves the superblock cleanup before closing the block
    device, which is also consistent with other callers. We also don't
    need a private copy of dev_name as the whole routine operates under
    the uuid_mutex.

    Signed-off-by: Jeff Mahoney <jeffm@suse.com>
    Reviewed-by: David Sterba <dsterba@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/btrfs/volumes.c | 38 +++++++++++---------------------------
    1 file changed, 11 insertions(+), 27 deletions(-)

    --- a/fs/btrfs/volumes.c
    +++ b/fs/btrfs/volumes.c
    @@ -1846,7 +1846,6 @@ int btrfs_rm_device(struct btrfs_root *r
    u64 num_devices;
    int ret = 0;
    bool clear_super = false;
    - char *dev_name = NULL;

    mutex_lock(&uuid_mutex);

    @@ -1882,11 +1881,6 @@ int btrfs_rm_device(struct btrfs_root *r
    list_del_init(&device->dev_alloc_list);
    device->fs_devices->rw_devices--;
    unlock_chunks(root);
    - dev_name = kstrdup(device->name->str, GFP_KERNEL);
    - if (!dev_name) {
    - ret = -ENOMEM;
    - goto error_undo;
    - }
    clear_super = true;
    }

    @@ -1936,14 +1930,21 @@ int btrfs_rm_device(struct btrfs_root *r
    btrfs_sysfs_rm_device_link(root->fs_info->fs_devices, device);
    }

    - btrfs_close_bdev(device);
    -
    - call_rcu(&device->rcu, free_device);
    -
    num_devices = btrfs_super_num_devices(root->fs_info->super_copy) - 1;
    btrfs_set_super_num_devices(root->fs_info->super_copy, num_devices);
    mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

    + /*
    + * at this point, the device is zero sized and detached from
    + * the devices list. All that's left is to zero out the old
    + * supers and free the device.
    + */
    + if (device->writeable)
    + btrfs_scratch_superblocks(device->bdev, device->name->str);
    +
    + btrfs_close_bdev(device);
    + call_rcu(&device->rcu, free_device);
    +
    if (cur_devices->open_devices == 0) {
    struct btrfs_fs_devices *fs_devices;
    fs_devices = root->fs_info->fs_devices;
    @@ -1962,24 +1963,7 @@ int btrfs_rm_device(struct btrfs_root *r
    root->fs_info->num_tolerated_disk_barrier_failures =
    btrfs_calc_num_tolerated_disk_barrier_failures(root->fs_info);

    - /*
    - * at this point, the device is zero sized. We want to
    - * remove it from the devices list and zero out the old super
    - */
    - if (clear_super) {
    - struct block_device *bdev;
    -
    - bdev = blkdev_get_by_path(dev_name, FMODE_READ | FMODE_EXCL,
    - root->fs_info->bdev_holder);
    - if (!IS_ERR(bdev)) {
    - btrfs_scratch_superblocks(bdev, dev_name);
    - blkdev_put(bdev, FMODE_READ | FMODE_EXCL);
    - }
    - }
    -
    out:
    - kfree(dev_name);
    -
    mutex_unlock(&uuid_mutex);
    return ret;


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