[RFC PATCH] dax, ext2, ext4, XFS: fix data corruption race

[Matthew Wilcox]

On Fri, Jan 22, 2016 at 04:06:11PM -0700, Ross Zwisler wrote:
> +++ b/fs/block_dev.c
> @@ -1733,13 +1733,28 @@ static const struct address_space_operations def_blk_aops = {
>   */
>  static int blkdev_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> -	return __dax_fault(vma, vmf, blkdev_get_block, NULL);
> +	int ret;
> +
> +	ret = __dax_fault(vma, vmf, blkdev_get_block, NULL, false);
> +
> +	if (WARN_ON_ONCE(ret == -EAGAIN))
> +		ret = VM_FAULT_SIGBUS;
> +
> +	return ret;
>  }

Let's not mix up -E returns and VM_FAULT returns.  We already have a
perfectly good VM_FAULT return value -- VM_FAULT_RETRY.