Re: [PATCH] block: protect iterate_bdevs() against concurrent close

From: Rabin Vincent
Date: Mon Mar 14 2016 - 13:43:48 EST

(fixed Jens' address)

On Thu, Mar 10, 2016 at 06:37:27PM +0100, Jan Kara wrote:
> On Thu 10-03-16 13:26:03, Rabin Vincent wrote:
> > If a block device is closed while iterate_bdevs() is handling it, the
> > following NULL pointer dereference occurs because bdev->b_disk is NULL
> > in bdev_get_queue(), which is called from blk_get_backing_dev_info() (in
> > turn called by the mapping_cap_writeback_dirty() call in
> > __filemap_fdatawrite_range()):
> Thanks for spotting the problem. The patch will fix the problem you
> found. But what prevents e.g. flusher thread from trying to writeback
> the block device inode while that gets invalidated at the same moment?

Don't the sync_block_dev() / bdev_write_inode() calls in __blkdev_put()
prevent this?