kernfs: remove KERNFS_ACTIVE_REF and add kernfs_lockdep()

There currently are two mechanisms gating active ref lockdep
annotations - KERNFS_LOCKDEP flag and KERNFS_ACTIVE_REF type mask.
The former disables lockdep annotations in kernfs_get/put_active()
while the latter disables all of kernfs_deactivate().

While KERNFS_ACTIVE_REF also behaves as an optimization to skip the
deactivation step for non-file nodes, the benefit is marginal and it
needlessly diverges code paths.  Let's drop KERNFS_ACTIVE_REF and use
KERNFS_LOCKDEP in kernfs_deactivate() too.

While at it, add a test helper kernfs_lockdep() to test KERNFS_LOCKDEP
flag so that it's more convenient and the related code can be compiled
out when not enabled.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 20 insertions, 11 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index ed62de6cdf8f..1c9130a33048 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -22,6 +22,15 @@ DEFINE_MUTEX(kernfs_mutex);
 
 #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
 
+static bool kernfs_lockdep(struct kernfs_node *kn)
+{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+        return kn->flags & KERNFS_LOCKDEP;
+#else
+        return false;
+#endif
+}
+
 /**
  *      kernfs_name_hash
  *      @name: Null terminated string to hash
@@ -138,7 +147,7 @@ struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
         if (!atomic_inc_unless_negative(&kn->active))
                 return NULL;
 
-        if (kn->flags & KERNFS_LOCKDEP)
+        if (kernfs_lockdep(kn))
                 rwsem_acquire_read(&kn->dep_map, 0, 1, _RET_IP_);
         return kn;
 }
@@ -158,7 +167,7 @@ void kernfs_put_active(struct kernfs_node *kn)
         if (unlikely(!kn))
                 return;
 
-        if (kn->flags & KERNFS_LOCKDEP)
+        if (kernfs_lockdep(kn))
                 rwsem_release(&kn->dep_map, 1, _RET_IP_);
         v = atomic_dec_return(&kn->active);
         if (likely(v != KN_DEACTIVATED_BIAS))
@@ -179,21 +188,21 @@ static void kernfs_deactivate(struct kernfs_node *kn)
 
         BUG_ON(!(kn->flags & KERNFS_REMOVED));
 
-        if (!(kernfs_type(kn) & KERNFS_ACTIVE_REF))
-                return;
-
-        rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
-
         atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
 
-        if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
-                lock_contended(&kn->dep_map, _RET_IP_);
+        if (kernfs_lockdep(kn)) {
+                rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
+                if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
+                        lock_contended(&kn->dep_map, _RET_IP_);
+        }
 
         wait_event(root->deactivate_waitq,
                    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
 
-        lock_acquired(&kn->dep_map, _RET_IP_);
-        rwsem_release(&kn->dep_map, 1, _RET_IP_);
+        if (kernfs_lockdep(kn)) {
+                lock_acquired(&kn->dep_map, _RET_IP_);
+                rwsem_release(&kn->dep_map, 1, _RET_IP_);
+        }
 }
 
 /**