From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753948AbdLMVwQ (ORCPT ); Wed, 13 Dec 2017 16:52:16 -0500 Received: from mail.kernel.org ([198.145.29.99]:54926 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753879AbdLMVwN (ORCPT ); Wed, 13 Dec 2017 16:52:13 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EBC6120836 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=jlayton@kernel.org Message-ID: <1513201930.3498.37.camel@kernel.org> Subject: Re: [PATCH 02/19] fs: don't take the i_lock in inode_inc_iversion From: Jeff Layton To: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, hch@lst.de, neilb@suse.de, bfields@fieldses.org, amir73il@gmail.com, jack@suse.de, viro@zeniv.linux.org.uk Date: Wed, 13 Dec 2017 16:52:10 -0500 In-Reply-To: <20171213142017.23653-3-jlayton@kernel.org> References: <20171213142017.23653-1-jlayton@kernel.org> <20171213142017.23653-3-jlayton@kernel.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.2 (3.26.2-1.fc27) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2017-12-13 at 09:20 -0500, Jeff Layton wrote: > From: Jeff Layton > > The rationale for taking the i_lock when incrementing this value is > lost in antiquity. The readers of the field don't take it (at least > not universally), so my assumption is that it was only done here to > serialize incrementors. > > If that is indeed the case, then we can drop the i_lock from this > codepath and treat it as a atomic64_t for the purposes of > incrementing it. This allows us to use inode_inc_iversion without > any danger of lock inversion. > > Note that the read side is not fetched atomically with this change. > The assumption here is that that is not a critical issue since the > i_version is not fully synchronized with anything else anyway. > > Signed-off-by: Jeff Layton > --- > include/linux/fs.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 5001e77342fd..c234fac4bb77 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -2136,9 +2136,9 @@ inode_set_iversion_queried(struct inode *inode, const u64 new) > static inline bool > inode_maybe_inc_iversion(struct inode *inode, bool force) > { > - spin_lock(&inode->i_lock); > - inode->i_version++; > - spin_unlock(&inode->i_lock); > + atomic64_t *ivp = (atomic64_t *)&inode->i_version; > + > + atomic64_inc(ivp); > return true; > } > FWIW, I'm not sure this patch is strictly necessary as an interim step. Adding the i_lock into the all of the places where we currently just do inode->i_version++ without properly auditing all of them gave me pause though. In any case, the last patch in the series cleans this nastiness up. -- Jeff Layton