Re: [PATCH 1/8] xfs: mmap lock needs to be inside freeze protection

[Brian Foster <bfoster@redhat.com>]

On Tue, Mar 24, 2015 at 09:50:59PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Lock ordering for the new mmap lock needs to be:
> 
> mmap_sem
>   sb_start_pagefault
>     i_mmap_lock
>       page lock
>         <fault processsing>
> 
> Right now xfs_vm_page_mkwrite gets this the wrong way around,
> While technically it cannot deadlock due to the current freeze
> ordering, it's still a landmine that might explode if we change
> anything in future. Hence we need to nest the locks correctly.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

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

>  fs/xfs/xfs_file.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index dc5f609..a4c882e 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1449,15 +1449,20 @@ xfs_filemap_page_mkwrite(
>  	struct vm_fault		*vmf)
>  {
>  	struct xfs_inode	*ip = XFS_I(vma->vm_file->f_mapping->host);
> -	int			error;
> +	int			ret;
>  
>  	trace_xfs_filemap_page_mkwrite(ip);
>  
> +	sb_start_pagefault(VFS_I(ip)->i_sb);
> +	file_update_time(vma->vm_file);
>  	xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
> -	error = block_page_mkwrite(vma, vmf, xfs_get_blocks);
> +
> +	ret = __block_page_mkwrite(vma, vmf, xfs_get_blocks);
> +
>  	xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
> +	sb_end_pagefault(VFS_I(ip)->i_sb);
>  
> -	return error;
> +	return block_page_mkwrite_return(ret);
>  }
>  
>  const struct file_operations xfs_file_operations = {
> -- 
> 2.0.0
> 
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