Re: [PATCH 6/6] xfs: xfs_filemap_pmd_fault treats read faults as write faults

Brian Foster
2015-10-29T14:30:09Z

On Mon, Oct 19, 2015 at 02:27:18PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> The code initially committed didn't have the same checks for write
> faults as the dax_pmd_fault code and hence treats all faults as
> write faults. We can get read faults through this path because they
> is no pmd_mkwrite path for write faults similar to the normal page
> fault path. Hence we need to ensure that we only do c/mtime updates
> on write faults, and freeze protection is unnecessary for read
> faults.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

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

> fs/xfs/xfs_file.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index e7cf9ec..0045b0a 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1482,7 +1482,7 @@ xfs_file_llseek(
> *
> * mmap_sem (MM)
> * sb_start_pagefault(vfs, freeze)
> - * i_mmap_lock (XFS - truncate serialisation)
> + * i_mmaplock (XFS - truncate serialisation)
> * page_lock (MM)
> * i_lock (XFS - extent map serialisation)
> */
> @@ -1550,6 +1550,13 @@ xfs_filemap_fault(
> return ret;
> }
>
> +/*
> + * Similar to xfs_filemap_fault(), the DAX fault path can call into here on
> + * both read and write faults. Hence we need to handle both cases. There is no
> + * ->pmd_mkwrite callout for huge pages, so we have a single function here to
> + * handle both cases here. @flags carries the information on the type of fault
> + * occuring.
> + */
> STATIC int
> xfs_filemap_pmd_fault(
> struct vm_area_struct *vma,
> @@ -1566,13 +1573,18 @@ xfs_filemap_pmd_fault(
>
> trace_xfs_filemap_pmd_fault(ip);
>
> - sb_start_pagefault(inode->i_sb);
> - file_update_time(vma->vm_file);
> + if (flags & FAULT_FLAG_WRITE) {
> + sb_start_pagefault(inode->i_sb);
> + file_update_time(vma->vm_file);
> + }
> +
> xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> ret = __dax_pmd_fault(vma, addr, pmd, flags, xfs_get_blocks_dax_fault,
> NULL);
> xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> - sb_end_pagefault(inode->i_sb);
> +
> + if (flags & FAULT_FLAG_WRITE)
> + sb_end_pagefault(inode->i_sb);
>
> return ret;
> }
> --
> 2.5.0
>
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