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

Brian Foster
2015-10-29T14:30:06Z

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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