Re: [PATCH v2] Do a proper locking for mmap and block size change

Dave Chinner
2012-11-30T02:49:15Z

On Thu, Nov 29, 2012 at 02:16:50PM -0800, Linus Torvalds wrote:
> On Thu, Nov 29, 2012 at 1:29 PM, Chris Mason <chris.mason@fusionio.com> wrote:
> >
> > Just reading the new blkdev_get_blocks, it looks like we're mixing
> > shifts. In direct-io.c map_bh->b_size is how much we'd like to map, and
> > it has no relation at all to the actual block size of the device. The
> > interface is abusing b_size to ask for as large a mapping as possible.
>
> Ugh. That's a big violation of how buffer-heads are supposed to work:
> the block number is very much defined to be in multiples of b_size
> (see for example "submit_bh()" that turns it into a sector number).
>
> But you're right. The direct-IO code really *is* violating that, and
> knows that get_block() ends up being defined in i_blkbits regardless
> of b_size.

Same with mpage_readpages(), so it's not just direct IO that has
this problem....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com