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Re: [PATCH 3/6] xfs: use i_mmaplock on write faults

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/6] xfs: use i_mmaplock on write faults
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Mon, 9 Feb 2015 15:31:28 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1423083859-28439-4-git-send-email-david@xxxxxxxxxxxxx>
References: <1423083859-28439-1-git-send-email-david@xxxxxxxxxxxxx> <1423083859-28439-4-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Thu, Feb 05, 2015 at 08:04:16AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> Take the i_mmaplock over write page faults. These come through the
> ->page_mkwrite callout, so we need to wrap that calls with the
> i_mmaplock.
> 
> This gives us a lock order of mmap_sem -> i_mmaplock -> page_lock
> -> i_lock.
> 
> Also, move the page_mkwrite wrapper to the same region of xfs_file.c
> as the read fault wrappers and add a tracepoint.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---

Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>

>  fs/xfs/xfs_file.c  | 39 ++++++++++++++++++++++++---------------
>  fs/xfs/xfs_trace.h |  1 +
>  2 files changed, 25 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 6cc1b7d..2bb25fd 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -981,20 +981,6 @@ xfs_file_mmap(
>  }
>  
>  /*
> - * mmap()d file has taken write protection fault and is being made
> - * writable. We can set the page state up correctly for a writable
> - * page, which means we can do correct delalloc accounting (ENOSPC
> - * checking!) and unwritten extent mapping.
> - */
> -STATIC int
> -xfs_vm_page_mkwrite(
> -     struct vm_area_struct   *vma,
> -     struct vm_fault         *vmf)
> -{
> -     return block_page_mkwrite(vma, vmf, xfs_get_blocks);
> -}
> -
> -/*
>   * This type is designed to indicate the type of offset we would like
>   * to search from page cache for xfs_seek_hole_data().
>   */
> @@ -1395,6 +1381,29 @@ xfs_filemap_fault(
>       return error;
>  }
>  
> +/*
> + * mmap()d file has taken write protection fault and is being made writable. 
> We
> + * can set the page state up correctly for a writable page, which means we 
> can
> + * do correct delalloc accounting (ENOSPC checking!) and unwritten extent
> + * mapping.
> + */
> +STATIC int
> +xfs_filemap_page_mkwrite(
> +     struct vm_area_struct   *vma,
> +     struct vm_fault         *vmf)
> +{
> +     struct xfs_inode        *ip = XFS_I(vma->vm_file->f_mapping->host);
> +     int                     error;
> +
> +     trace_xfs_filemap_page_mkwrite(ip);
> +
> +     xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
> +     error = block_page_mkwrite(vma, vmf, xfs_get_blocks);
> +     xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
> +
> +     return error;
> +}
> +
>  const struct file_operations xfs_file_operations = {
>       .llseek         = xfs_file_llseek,
>       .read           = new_sync_read,
> @@ -1429,6 +1438,6 @@ const struct file_operations xfs_dir_file_operations = {
>  static const struct vm_operations_struct xfs_file_vm_ops = {
>       .fault          = xfs_filemap_fault,
>       .map_pages      = filemap_map_pages,
> -     .page_mkwrite   = xfs_vm_page_mkwrite,
> +     .page_mkwrite   = xfs_filemap_page_mkwrite,
>       .remap_pages    = generic_file_remap_pages,
>  };
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index c496153..b1e059b 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -686,6 +686,7 @@ DEFINE_INODE_EVENT(xfs_inode_clear_eofblocks_tag);
>  DEFINE_INODE_EVENT(xfs_inode_free_eofblocks_invalid);
>  
>  DEFINE_INODE_EVENT(xfs_filemap_fault);
> +DEFINE_INODE_EVENT(xfs_filemap_page_mkwrite);
>  
>  DECLARE_EVENT_CLASS(xfs_iref_class,
>       TP_PROTO(struct xfs_inode *ip, unsigned long caller_ip),
> -- 
> 2.0.0
> 
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