Re: [PATCH 3/8] xfs: flush page mappings as part of setting immutable

Brian Foster
2019-04-26T18:18:05Z

On Wed, Apr 17, 2019 at 12:04:47PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.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
> immutable flag so that all mappings will become read-only again and
> therefore programs cannot continue to write to writable mappings.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
> fs/xfs/xfs_ioctl.c | 52 +++++++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 45 insertions(+), 7 deletions(-)
>
>
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 21d6f433c375..de35cf4469f6 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1009,6 +1009,31 @@ xfs_diflags_to_linux(
> #endif
> }
>
> +/*
> + * Lock the inode against file io and page faults, then flush all dirty pages
> + * and wait for writeback and direct IO operations to finish. Returns with
> + * the relevant inode lock flags set in @join_flags. Caller is responsible for
> + * unlocking even on error return.
> + */
> +static int
> +xfs_ioctl_setattr_flush(
> + struct xfs_inode *ip,
> + int *join_flags)
> +{
> + struct inode *inode = VFS_I(ip);
> +
> + /* Already locked the inode from IO? Assume we're done. */
> + if (((*join_flags) & (XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL)) ==
> + (XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL))
> + return 0;
> +

Ok, so I take it this is because the xfs_setattr_path() can call down
into here via dax_invalidate() and then subsequently via the immutable
check. Instead of burying this down here, could we just check join_flags
!= 0 prior to the second setattr_flush() call? Otherwise this looks Ok
to me.

Brian

> + /* Lock and flush all mappings and IO in preparation for flag change */
> + *join_flags = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
> + xfs_ilock(ip, *join_flags);
> + inode_dio_wait(inode);
> + return filemap_write_and_wait(inode->i_mapping);
> +}
> +
> static int
> xfs_ioctl_setattr_xflags(
> struct xfs_trans *tp,
> @@ -1103,25 +1128,22 @@ xfs_ioctl_setattr_dax_invalidate(
> if (!(fa->fsx_xflags & FS_XFLAG_DAX) && !IS_DAX(inode))
> return 0;
>
> - if (S_ISDIR(inode->i_mode))
> + if (!S_ISREG(inode->i_mode))
> 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);
> + error = xfs_ioctl_setattr_flush(ip, join_flags);
> 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);
> + xfs_iunlock(ip, *join_flags);
> + *join_flags = 0;
> return error;
> -
> }
>
> /*
> @@ -1367,6 +1389,22 @@ xfs_ioctl_setattr(
> if (code)
> goto error_free_dquots;
>
> + /*
> + * Wait for all pending directio and then flush all the dirty pages
> + * for this file. The flush marks all the pages readonly, so any
> + * subsequent attempt to write to the file (particularly mmap pages)
> + * will come through the filesystem and fail.
> + */
> + if (S_ISREG(VFS_I(ip)->i_mode) && !IS_IMMUTABLE(VFS_I(ip)) &&
> + (fa->fsx_xflags & FS_XFLAG_IMMUTABLE)) {
> + code = xfs_ioctl_setattr_flush(ip, &join_flags);
> + if (code) {
> + xfs_iunlock(ip, join_flags);
> + join_flags = 0;
> + goto error_free_dquots;
> + }
> + }
> +
> tp = xfs_ioctl_setattr_get_trans(ip, join_flags);
> if (IS_ERR(tp)) {
> code = PTR_ERR(tp);
>