From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:35752 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779AbeFVG3J (ORCPT ); Fri, 22 Jun 2018 02:29:09 -0400 Date: Thu, 21 Jun 2018 23:29:07 -0700 From: Christoph Hellwig Subject: Re: [PATCH 8/8] xfs: ensure post-EOF zeroing happens after zeroing part of a file Message-ID: <20180622062907.GA27254@infradead.org> References: <152960586416.26246.8634761888260524091.stgit@magnolia> <152960591330.26246.305971181988789033.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <152960591330.26246.305971181988789033.stgit@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org On Thu, Jun 21, 2018 at 11:31:53AM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong > > If a user asks us to zero_range part of a file, the end of the range is > EOF, and not aligned to a page boundary, invoke writeback of the EOF > page to ensure that the post-EOF part of the page is zeroed. This > ensures that we don't expose stale memory contents via mmap, if in a > clumsy manner. > > Found by running generic/127 when it runs zero_range and mapread at EOF > one after the other. > > Signed-off-by: Darrick J. Wong > --- > fs/xfs/xfs_bmap_util.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > > diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c > index abc37b0899c0..c94d376e4152 100644 > --- a/fs/xfs/xfs_bmap_util.c > +++ b/fs/xfs/xfs_bmap_util.c > @@ -1208,7 +1208,20 @@ xfs_free_file_space( > return 0; > if (offset + len > XFS_ISIZE(ip)) > len = XFS_ISIZE(ip) - offset; > - return iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops); > + error = iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops); > + if (error) > + return error; > + > + /* > + * If we zeroed right up to EOF and EOF straddles a page boundary we > + * must make sure that the post-EOF area is also zeroed because the > + * page could be mmap'd and iomap_zero_range doesn't do that for us. > + * Writeback of the eof page will do this, albeit clumsily. > + */ > + if (offset + len < XFS_ISIZE(ip) || ((offset + len) & PAGE_MASK) == 0) > + return 0; > + return filemap_write_and_wait_range(VFS_I(ip)->i_mapping, > + (offset + len) & ~PAGE_MASK, LLONG_MAX); Total nitpick, but between the kernel logic flow and comment I'd invert the check: if (offset + len >= XFS_ISIZE(ip) && (offset + len) & PAGE_MASK) { error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping, (offset + len) & ~PAGE_MASK, LLONG_MAX); } return error; Otherwise looks good: Reviewed-by: Christoph Hellwig