Re: [dm-devel] [PATCH v2] dm mpath: maintain reference count for underlying devices

["Jun'ichi Nomura" <j-nomura ce jp nec com>]

On 10/18/11 05:15, Mike Snitzer wrote:
> FYI, this patch from Tejun should also fix the concern I had relative to
> mpath's underlying devices' request_queues:
> https://lkml.org/lkml/2011/10/16/148

Oh, that's good information.

Since the following commit, a queue can be accessed
after the device being released:

  commit f758eeabeb96f878c860e8f110f94ec8820822a9
  Author: Christoph Hellwig <hch infradead org>
  Date:   Thu Apr 21 18:19:44 2011 -0600

    writeback: split inode_wb_list_lock into bdi_writeback.list_lock

I.e.
  __blkdev_put
    disk->fops->release()
    ..
    bdev_inode_switch_bdi()
      bdi_lock_two()
      [access to bdev->bd_inode->i_data.backing_dev_info]

I think Tejun's patch is reasonable.

Thanks,
-- 
Jun'ichi Nomura, NEC Corporation