1 files changed, 38 insertions, 4 deletions
diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
index c4840ce..a21af4f 100644
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -353,6 +353,41 @@ compute_cn_lkflags(struct mount *mp, int lkflags)
 	return (lkflags);
 }
 
+static __inline int
+needs_exclusive_leaf(struct mount *mp, int flags)
+{
+
+	/*
+	 * Intermediate nodes can use shared locks, we only need to
+	 * force an exclusive lock for leaf nodes.
+	 */
+	if ((flags & (ISLASTCN | LOCKLEAF)) != (ISLASTCN | LOCKLEAF))
+		return (0);
+
+	/* Always use exclusive locks if LOCKSHARED isn't set. */
+	if (!(flags & LOCKSHARED))
+		return (1);
+
+	/*
+	 * For lookups during open(), if the mount point supports
+	 * extended shared operations, then use a shared lock for the
+	 * leaf node, otherwise use an exclusive lock.
+	 */
+	if (flags & ISOPEN) {
+		if (mp != NULL &&
+		    (mp->mnt_kern_flag & MNTK_EXTENDED_SHARED))
+			return (0);
+		else
+			return (1);
+	}
+
+	/*
+	 * Lookup requests outside of open() that specify LOCKSHARED
+	 * only need a shared lock on the leaf vnode.
+	 */
+	return (1);
+}
+
 /*
  * Search a pathname.
  * This is a very central and rather complicated routine.
@@ -610,8 +645,7 @@ unionlookup:
 	 * If we're looking up the last component and we need an exclusive
 	 * lock, adjust our lkflags.
 	 */
-	if ((cnp->cn_flags & (ISLASTCN|LOCKSHARED|LOCKLEAF)) ==
-	    (ISLASTCN|LOCKLEAF))
+	if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags))
 		cnp->cn_lkflags = LK_EXCLUSIVE;
 #ifdef NAMEI_DIAGNOSTIC
 	vprint("lookup in", dp);
@@ -811,8 +845,8 @@ success:
 	 * Because of lookup_shared we may have the vnode shared locked, but
 	 * the caller may want it to be exclusively locked.
 	 */
-	if ((cnp->cn_flags & (ISLASTCN | LOCKSHARED | LOCKLEAF)) ==
-	    (ISLASTCN | LOCKLEAF) && VOP_ISLOCKED(dp) != LK_EXCLUSIVE) {
+	if (needs_exclusive_leaf(dp->v_mount, cnp->cn_flags) &&
+	    VOP_ISLOCKED(dp) != LK_EXCLUSIVE) {
 		vn_lock(dp, LK_UPGRADE | LK_RETRY);
 		if (dp->v_iflag & VI_DOOMED) {
 			error = ENOENT;