[PATCH 06/12] kernfs: remove KERNFS_ACTIVE_REF and add kernfs_lockdep()

[Tejun Heo]

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@xxxxxxxxxx>
---
 fs/kernfs/dir.c        | 30 ++++++++++++++++++++----------
 include/linux/kernfs.h |  1 -
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 07cf22c..8abdf07 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
@@ -144,7 +153,7 @@ 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;
 }
@@ -164,7 +173,7 @@ 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))
@@ -190,25 +199,26 @@ static void kernfs_deactivate(struct kernfs_node *kn)
 	lockdep_assert_held(&kernfs_mutex);
 	BUG_ON(!(kn->flags & KERNFS_REMOVED));
 
-	if (!(kernfs_type(kn) & KERNFS_ACTIVE_REF))
-		return;
-
 	/* only the first invocation on @kn should deactivate it */
 	if (atomic_read(&kn->active) >= 0)
 		atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
 
 	mutex_unlock(&kernfs_mutex);
 
-	rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
-	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_);
+	}
 
 	/* but everyone should wait for draining */
 	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_);
+	}
 
 	kernfs_unmap_bin_file(kn);
 
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 4b68b6f..bff6e08 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -34,7 +34,6 @@ enum kernfs_node_type {
 };
 
 #define KERNFS_TYPE_MASK	0x000f
-#define KERNFS_ACTIVE_REF	KERNFS_FILE
 #define KERNFS_FLAG_MASK	~KERNFS_TYPE_MASK
 
 enum kernfs_node_flag {
-- 
1.8.4.2

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