Re: [PATCH] kill superflous buffer locking

[Christoph Hellwig <hch@lst.de>]

On Wed, Nov 28, 2007 at 01:30:18PM +1100, Lachlan McIlroy wrote:
> Christoph,
> 
> We've fixed the source of the assertion (that was the bugs in
> xfs_buf_associate_memory()) so I'm pushing your buffer lock
> removal patch back in again.
> 
> While looking through it I found a couple of issues:
> 
> - It called unlock_page() before calls to PagePrivate() and
>   PageUptodate().  I think the page needs to be locked during
>   these calls so I moved the unlock_page() further down.

This doesn't really matter at all.  XFS is the only user of the
address_space the pages reside in and we never have overlapping
buffers.  That's the reason why we can remove the buffer locking.
Now if there was a variant of find_or_create_page that didn't set
pages locked at all we could happily use it and get rid of the last
place we deal with locked pages.

> - Unlocking the pages as we go can cause a double unlock in the
>   error handling for a NULL page in the XBF_READ_AHEAD case so I
>   removed the unlocking code for that case.

Indeed.  Thanks for spotting this.