Re: [PATCH 1/7] xfs: don't dirty buffers beyond EOF

Dave Chinner
2014-08-28T22:37:11Z

On Thu, Aug 28, 2014 at 09:34:57AM -0400, Brian Foster wrote:
> On Thu, Aug 28, 2014 at 09:49:05PM +1000, Dave Chinner wrote:
> > +/*
> > + * This is basically a copy of __set_page_dirty_buffers() with one
> > + * small tweak: buffers beyond EOF do not get marked dirty. If we mark them
> > + * dirty, we'll never be able to clean them because we don't write buffers
> > + * beyond EOF, and that means we can't invalidate pages that span EOF
> > + * that have been marked dirty. Further, the dirty state can leak into
> > + * the file interior if the file is extended, resulting in all sorts of
> > + * bad things happening as the state does not match the unerlying data.
> > + */
> > +STATIC int
> > +xfs_vm_set_page_dirty(
> > + struct page *page)
> > +{
> > + struct address_space *mapping = page->mapping;
> > + struct inode *inode = mapping->host;
> > + loff_t end_offset;
> > + loff_t offset;
> > + int newly_dirty;
> > +
> > + if (unlikely(!mapping))
> > + return !TestSetPageDirty(page);
> > +
> > + end_offset = i_size_read(inode);
> > + offset = end_offset & PAGE_CACHE_MASK;
>
> Is this what you intended to do here?
>
> offset = page_offset(page);

Yup, that's a bug. Which points out just how important the buffer
dirty flag is (not) to XFS, doesn't it?

I'll post a fixed patch in a few minutes after it's run a few
tens of millions fsx ops...

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com