linux-ext4 - Re: [PATCH 2/3] xfs: reset page mappings after setting immutable

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Date:   Fri, 29 Mar 2019 08:21:47 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/3] xfs: reset page mappings after setting immutable

On Thu, Mar 28, 2019 at 10:50:47AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@...cle.com>
> 
> The chattr manpage has this to say about immutable files:
> 
> "A file with the 'i' attribute cannot be modified: it cannot be deleted
> or renamed, no link can be created to this file, most of the file's
> metadata can not be modified, and the file can not be opened in write
> mode."
> 
> This means that we need to flush the page cache when setting the

nit: flush and invalidate the page cache.

> immutable flag so that programs cannot continue to write to writable
> mappings.

Do we even need to invalidate the page cache for this? i.e. we've
cleaned the pages so that any new write to them will fault,
that will see the immutable flag via ->page_mkwrite and then the
app should segv, right?

> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
>  fs/xfs/xfs_ioctl.c |   63 +++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 43 insertions(+), 20 deletions(-)
> 
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 6ecdbb3af7de..2bd1c5ab5008 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -998,6 +998,37 @@ xfs_diflags_to_linux(
>  #endif
>  }
>  
> +static int
> +xfs_ioctl_setattr_flush(
> +	struct xfs_inode	*ip,
> +	int			*join_flags)
> +{
> +	struct inode		*inode = VFS_I(ip);
> +	int			error;
> +
> +	if (S_ISDIR(inode->i_mode))
> +		return 0;
> +	if ((*join_flags) & (XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL))
> +		return 0;
> +
> +	/* lock, flush and invalidate mapping in preparation for flag change */
> +	xfs_ilock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
> +	error = filemap_write_and_wait(inode->i_mapping);
> +	if (error)
> +		goto out_unlock;
> +	error = invalidate_inode_pages2(inode->i_mapping);
> +	if (error)
> +		goto out_unlock;
> +
> +	*join_flags = XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL;
> +	return 0;
> +
> +out_unlock:
> +	xfs_iunlock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
> +	return error;
> +
> +}

Doesn't wait for direct IO to drain. Wouldn't it be better to do
this?

	lock()
	xfs_flush_unmap_range(ip, 0, XFS_SIZE(ip));
	unlock()

Otherwise looks ok.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com