From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:44960 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726449AbfEINFn (ORCPT ); Thu, 9 May 2019 09:05:43 -0400 Date: Thu, 9 May 2019 09:05:39 -0400 From: Brian Foster Subject: Re: [PATCH] xfs: short circuit xfs_get_acl() if no acl is possible Message-ID: <20190509130535.GB41691@bfoster> References: <35128e32-d69b-316e-c8d6-8f109646390d@redhat.com> <20190508201033.GW5207@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190508201033.GW5207@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: Eric Sandeen , linux-xfs , David Valin On Wed, May 08, 2019 at 01:10:33PM -0700, Darrick J. Wong wrote: > On Wed, May 08, 2019 at 02:28:09PM -0500, Eric Sandeen wrote: > > If there are no attributes on the inode, don't go through the > > cost of memory allocation and callling xfs_attr_get when we > > already know we'll just get -ENOATTR. > > > > Reported-by: David Valin > > Suggested-by: Dave Chinner > > Signed-off-by: Eric Sandeen > > --- > > > > diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c > > index 8039e35147dd..b469b44e9e71 100644 > > --- a/fs/xfs/xfs_acl.c > > +++ b/fs/xfs/xfs_acl.c > > @@ -132,6 +132,9 @@ xfs_get_acl(struct inode *inode, int type) > > BUG(); > > } > > > > + if (!xfs_inode_hasattr(ip)) > > + return NULL; > > This isn't going to cause problems if someone's adding an ACL to the > inode at the same time, right? > > I'm assuming that's the case since we only would load inodes when > setting up a vfs inode but before any userspace can get its sticky > fingers all over the inode, but it sure would be nice to know that > for sure. :) > Hmm, that's a good question. At first I was thinking it wouldn't matter, but then I remembered the fairly recent issue around writing back an empty leaf buffer on format conversion a bit too early. That has me wondering if that would be an issue here as well. For example, suppose a non-empty local format attr fork is being converted to extent format due to a concurrent (and unrelated) xattr set. That involves xfs_attr_shortform_to_leaf() -> xfs_bmap_local_to_extents_empty(), which looks like it creates a transient empty fork state. Might xfs_inode_hasattr() catch that as a false negative here? If so, that would certainly be a problem if the existing xattr was the ACL the caller happens to be interested in. It might be prudent to surround this check with ILOCK_SHARED... Brian > --D > > > + > > /* > > * If we have a cached ACLs value just return it, not need to > > * go out to the disk. > >