[PATCH 03/14] kernfs: remove KERNFS_ACTIVE_REF and add kernfs_lockdep()

Tejun Heo
2014-01-10T13:50:48Z

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>
---
fs/kernfs/dir.c | 31 ++++++++++++++++++++-----------
include/linux/kernfs.h | 1 -
2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index ed62de6..1c9130a 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_);
+ }
}

/**
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 232f1a6..42ad32f 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