[PATCH] namei: Use READ_ONCE() for d_flags in __follow_mount_rcu()

[Ze Tan]

__follow_mount_rcu() reads dentry->d_flags without holding d_lock.

Use READ_ONCE() for these reads to make the lockless access clear.

Signed-off-by: Ze Tan <tanze@xxxxxxxxxx>
---
 fs/namei.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 19ce43c9a6e6..cc8e8d961d7e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1687,7 +1687,7 @@ EXPORT_SYMBOL(follow_down);
 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path)
 {
 	struct dentry *dentry = path->dentry;
-	unsigned int flags = dentry->d_flags;
+	unsigned int flags = READ_ONCE(dentry->d_flags);
 
 	if (unlikely(nd->flags & LOOKUP_NO_XDEV))
 		return false;
@@ -1701,7 +1701,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path)
 			int res = dentry->d_op->d_manage(path, true);
 			if (res)
 				return res == -EISDIR;
-			flags = dentry->d_flags;
+			flags = READ_ONCE(dentry->d_flags);
 		}
 
 		if (flags & DCACHE_MOUNTED) {
@@ -1711,7 +1711,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path)
 				dentry = path->dentry = mounted->mnt.mnt_root;
 				nd->state |= ND_JUMPED;
 				nd->next_seq = read_seqcount_begin(&dentry->d_seq);
-				flags = dentry->d_flags;
+				flags = READ_ONCE(dentry->d_flags);
 				// makes sure that non-RCU pathwalk could reach
 				// this state.
 				if (read_seqretry(&mount_lock, nd->m_seq))
-- 
2.43.0