Re: [PATCH 5/6] xfs: add ->pfn_mkwrite support for DAX

[Brian Foster <bfoster@redhat.com>]

On Mon, Oct 19, 2015 at 02:27:17PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> ->pfn_mkwrite support is needed so that when a page with allocated
> backing store takes a write fault we can check that the fault has
> not raced with a truncate and is pointing to a region beyond the
> current end of file.
> 
> This also allows us to update the timestamp on the inode, too, which
> fixes a generic/080 failure.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/xfs_file.c  | 35 +++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_trace.h |  1 +
>  2 files changed, 36 insertions(+)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 403151a..e7cf9ec 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1577,11 +1577,46 @@ xfs_filemap_pmd_fault(
>  	return ret;
>  }
>  
> +/*
> + * pfn_mkwrite was originally inteneded to ensure we capture time stamp
> + * updates on write faults. In reality, it's need to serialise against
> + * truncate similar to page_mkwrite. Hence we open-code dax_pfn_mkwrite()
> + * here and cycle the XFS_MMAPLOCK_SHARED to ensure we serialise the fault
> + * barrier in place.
> + */
> +static int
> +xfs_filemap_pfn_mkwrite(
> +	struct vm_area_struct	*vma,
> +	struct vm_fault		*vmf)
> +{
> +
> +	struct inode		*inode = file_inode(vma->vm_file);
> +	struct xfs_inode	*ip = XFS_I(inode);
> +	int			ret = VM_FAULT_NOPAGE;
> +	loff_t			size;
> +
> +	trace_xfs_filemap_pfn_mkwrite(ip);
> +
> +	sb_start_pagefault(inode->i_sb);
> +	file_update_time(vma->vm_file);
> +
> +	/* check if the faulting page hasn't raced with truncate */
> +	xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
> +	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> +	if (vmf->pgoff >= size)
> +		ret = VM_FAULT_SIGBUS;
> +	xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
> +	sb_end_pagefault(inode->i_sb);
> +	return ret;
> +
> +}
> +
>  static const struct vm_operations_struct xfs_file_vm_ops = {
>  	.fault		= xfs_filemap_fault,
>  	.pmd_fault	= xfs_filemap_pmd_fault,
>  	.map_pages	= filemap_map_pages,
>  	.page_mkwrite	= xfs_filemap_page_mkwrite,
> +	.pfn_mkwrite	= xfs_filemap_pfn_mkwrite,
>  };
>  
>  STATIC int
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index 957f5cc..877079eb 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -689,6 +689,7 @@ DEFINE_INODE_EVENT(xfs_inode_free_eofblocks_invalid);
>  DEFINE_INODE_EVENT(xfs_filemap_fault);
>  DEFINE_INODE_EVENT(xfs_filemap_pmd_fault);
>  DEFINE_INODE_EVENT(xfs_filemap_page_mkwrite);
> +DEFINE_INODE_EVENT(xfs_filemap_pfn_mkwrite);
>  
>  DECLARE_EVENT_CLASS(xfs_iref_class,
>  	TP_PROTO(struct xfs_inode *ip, unsigned long caller_ip),
> -- 
> 2.5.0
> 
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