[RFC][PATCH 3/5] overlayfs: Remove smp_mb__before_spinlock() usage

[Peter Zijlstra <peterz@infradead.org>]

[-- Attachment #1: peterz-overlayfs.patch --]
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While we could replace the smp_mb__before_spinlock() with the new
smp_mb__after_spinlock(), the normal pattern is to use
smp_store_release() to publish an object that is used for
lockless_dereference() -- and mirrors the regular rcu_assign_pointer()
/ rcu_dereference() patterns.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 fs/overlayfs/readdir.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -446,14 +446,14 @@ static int ovl_dir_fsync(struct file *fi
 
 			ovl_path_upper(dentry, &upperpath);
 			realfile = ovl_path_open(&upperpath, O_RDONLY);
-			smp_mb__before_spinlock();
+
 			inode_lock(inode);
 			if (!od->upperfile) {
 				if (IS_ERR(realfile)) {
 					inode_unlock(inode);
 					return PTR_ERR(realfile);
 				}
-				od->upperfile = realfile;
+				smp_store_release(&od->upperfile, realfile);
 			} else {
 				/* somebody has beaten us to it */
 				if (!IS_ERR(realfile))