From 7594c461161745f0d38a4346d4f895e0837b8094 Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton@redhat.com>
Date: Mon, 18 Dec 2017 06:25:31 -0500
Subject: [PATCH 05/24] fs: don't take the i_lock in inode_inc_iversion
Git-commit: 7594c461161745f0d38a4346d4f895e0837b8094
Patch-mainline: v4.16-rc1
References: bsc#1081186

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 <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Jan Kara <jack@suse.cz>

---
 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 d61e063f7c75..f268828f9f7e 100644
--- a/include/linux/iversion.h
+++ b/include/linux/iversion.h
@@ -110,12 +110,13 @@ 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
-- 
2.10.0