From: Jeff Layton Subject: [PATCH v5 02/19] fs: don't take the i_lock in inode_inc_iversion Date: Tue, 9 Jan 2018 09:10:42 -0500 Message-ID: <20180109141059.25929-3-jlayton@kernel.org> References: <20180109141059.25929-1-jlayton@kernel.org> Cc: linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-nfs@vger.kernel.org, bfields@fieldses.org, neilb@suse.de, jack@suse.de, linux-ext4@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca, linux-xfs@vger.kernel.org, darrick.wong@oracle.com, david@fromorbit.com, linux-btrfs@vger.kernel.org, clm@fb.com, jbacik@fb.com, dsterba@suse.com, linux-integrity@vger.kernel.org, zohar@linux.vnet.ibm.com, dmitry.kasatkin@gmail.com, linux-afs@lists.infradead.org, dhowells@redhat.com, jaltman@auristor.com, krzk@kernel.org To: linux-fsdevel@vger.kernel.org Return-path: In-Reply-To: <20180109141059.25929-1-jlayton@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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/iversion.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/include/linux/iversion.h b/include/linux/iversion.h index d09cc3a08740..5ad9eaa3a9b0 100644 --- a/include/linux/iversion.h +++ b/include/linux/iversion.h @@ -104,12 +104,13 @@ inode_set_iversion_queried(struct inode *inode, 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; } + /** * inode_inc_iversion - forcibly increment i_version * @inode: inode that needs to be updated -- 2.14.3