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Date: Mon, 3 Feb 2014 14:03:00 -0500
From: Tejun Heo <tj@...nel.org>
To: gregkh@...uxfoundation.org
Cc: linux-kernel@...r.kernel.org, schwidefsky@...ibm.com,
heiko.carstens@...ibm.com, stern@...land.harvard.edu,
JBottomley@...allels.com, bhelgaas@...gle.com,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 07/12] kernfs: remove KERNFS_REMOVED
KERNFS_REMOVED is used to mark half-initialized and dying nodes so
that they don't show up in lookups and deny adding new nodes under or
renaming it; however, its role overlaps that of deactivation.
It's necessary to deny addition of new children while removal is in
progress; however, this role considerably intersects with deactivation
- KERNFS_REMOVED prevents new children while deactivation prevents new
file operations. There's no reason to have them separate making
things more complex than necessary.
This patch removes KERNFS_REMOVED.
* Instead of KERNFS_REMOVED, each node now starts its life
deactivated. This means that we now use both atomic_add() and
atomic_sub() on KN_DEACTIVATED_BIAS, which is INT_MIN. The compiler
generates an overflow warnings when negating INT_MIN as the negation
can't be represented as a positive number. Nothing is actually
broken but let's bump BIAS by one to avoid the warnings for archs
which negates the subtrahend..
* A new helper kernfs_active() which tests whether kn->active >= 0 is
added for convenience and lockdep annotation. All KERNFS_REMOVED
tests are replaced with negated kernfs_active() tests.
* __kernfs_remove() is updated to deactivate, but not drain, all nodes
in the subtree instead of setting KERNFS_REMOVED. This removes
deactivation from kernfs_deactivate(), which is now renamed to
kernfs_drain().
* Sanity check on KERNFS_REMOVED in kernfs_put() is replaced with
checks on the active ref.
* Some comment style updates in the affected area.
v2: Reordered before removal path restructuring. kernfs_active()
dropped and kernfs_get/put_active() used instead. RB_EMPTY_NODE()
used in the lookup paths.
v3: Reverted most of v2 except for creating a new node with
KN_DEACTIVATED_BIAS.
Signed-off-by: Tejun Heo <tj@...nel.org>
---
fs/kernfs/dir.c | 66 ++++++++++++++++++++++++---------------------
fs/kernfs/kernfs-internal.h | 3 ++-
include/linux/kernfs.h | 1 -
3 files changed, 37 insertions(+), 33 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 5cf137b..d0fd739 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -22,6 +22,12 @@ DEFINE_MUTEX(kernfs_mutex);
#define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
+static bool kernfs_active(struct kernfs_node *kn)
+{
+ lockdep_assert_held(&kernfs_mutex);
+ return atomic_read(&kn->active) >= 0;
+}
+
static bool kernfs_lockdep(struct kernfs_node *kn)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -183,25 +189,20 @@ void kernfs_put_active(struct kernfs_node *kn)
}
/**
- * kernfs_deactivate - deactivate kernfs_node
- * @kn: kernfs_node to deactivate
+ * kernfs_drain - drain kernfs_node
+ * @kn: kernfs_node to drain
*
- * Deny new active references, drain existing ones and nuke all
- * existing mmaps. Mutiple removers may invoke this function
- * concurrently on @kn and all will return after deactivation and
- * draining are complete.
+ * Drain existing usages and nuke all existing mmaps of @kn. Mutiple
+ * removers may invoke this function concurrently on @kn and all will
+ * return after draining is complete.
*/
-static void kernfs_deactivate(struct kernfs_node *kn)
+static void kernfs_drain(struct kernfs_node *kn)
__releases(&kernfs_mutex) __acquires(&kernfs_mutex)
{
struct kernfs_root *root = kernfs_root(kn);
lockdep_assert_held(&kernfs_mutex);
- BUG_ON(!(kn->flags & KERNFS_REMOVED));
-
- /* only the first invocation on @kn should deactivate it */
- if (atomic_read(&kn->active) >= 0)
- atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
+ WARN_ON_ONCE(kernfs_active(kn));
mutex_unlock(&kernfs_mutex);
@@ -253,13 +254,15 @@ void kernfs_put(struct kernfs_node *kn)
return;
root = kernfs_root(kn);
repeat:
- /* Moving/renaming is always done while holding reference.
+ /*
+ * Moving/renaming is always done while holding reference.
* kn->parent won't change beneath us.
*/
parent = kn->parent;
- WARN(!(kn->flags & KERNFS_REMOVED), "kernfs: free using entry: %s/%s\n",
- parent ? parent->name : "", kn->name);
+ WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,
+ "kernfs_put: %s/%s: released with incorrect active_ref %d\n",
+ parent ? parent->name : "", kn->name, atomic_read(&kn->active));
if (kernfs_type(kn) == KERNFS_LINK)
kernfs_put(kn->symlink.target_kn);
@@ -301,8 +304,8 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
kn = dentry->d_fsdata;
mutex_lock(&kernfs_mutex);
- /* The kernfs node has been deleted */
- if (kn->flags & KERNFS_REMOVED)
+ /* The kernfs node has been deactivated */
+ if (!kernfs_active(kn))
goto out_bad;
/* The kernfs node has been moved? */
@@ -371,12 +374,12 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
kn->ino = ret;
atomic_set(&kn->count, 1);
- atomic_set(&kn->active, 0);
+ atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
RB_CLEAR_NODE(&kn->rb);
kn->name = name;
kn->mode = mode;
- kn->flags = flags | KERNFS_REMOVED;
+ kn->flags = flags;
return kn;
@@ -432,7 +435,7 @@ int kernfs_add_one(struct kernfs_node *kn)
goto out_unlock;
ret = -ENOENT;
- if (parent->flags & KERNFS_REMOVED)
+ if (!kernfs_active(parent))
goto out_unlock;
kn->hash = kernfs_name_hash(kn->name, kn->ns);
@@ -449,7 +452,7 @@ int kernfs_add_one(struct kernfs_node *kn)
}
/* Mark the entry added into directory tree */
- kn->flags &= ~KERNFS_REMOVED;
+ atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
ret = 0;
out_unlock:
mutex_unlock(&kernfs_mutex);
@@ -549,7 +552,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
return ERR_PTR(-ENOMEM);
}
- kn->flags &= ~KERNFS_REMOVED;
+ atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
kn->priv = priv;
kn->dir.root = root;
@@ -763,24 +766,25 @@ static void __kernfs_remove(struct kernfs_node *kn)
pr_debug("kernfs %s: removing\n", kn->name);
- /* disable lookup and node creation under @kn */
+ /* prevent any new usage under @kn by deactivating all nodes */
pos = NULL;
while ((pos = kernfs_next_descendant_post(pos, kn)))
- pos->flags |= KERNFS_REMOVED;
+ if (kernfs_active(pos))
+ atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
/* deactivate and unlink the subtree node-by-node */
do {
pos = kernfs_leftmost_descendant(kn);
/*
- * kernfs_deactivate() drops kernfs_mutex temporarily and
- * @pos's base ref could have been put by someone else by
- * the time the function returns. Make sure it doesn't go
- * away underneath us.
+ * kernfs_drain() drops kernfs_mutex temporarily and @pos's
+ * base ref could have been put by someone else by the time
+ * the function returns. Make sure it doesn't go away
+ * underneath us.
*/
kernfs_get(pos);
- kernfs_deactivate(pos);
+ kernfs_drain(pos);
/*
* kernfs_unlink_sibling() succeeds once per node. Use it
@@ -865,7 +869,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
mutex_lock(&kernfs_mutex);
error = -ENOENT;
- if ((kn->flags | new_parent->flags) & KERNFS_REMOVED)
+ if (!kernfs_active(kn) || !kernfs_active(new_parent))
goto out;
error = 0;
@@ -925,7 +929,7 @@ static struct kernfs_node *kernfs_dir_pos(const void *ns,
struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)
{
if (pos) {
- int valid = !(pos->flags & KERNFS_REMOVED) &&
+ int valid = kernfs_active(pos) &&
pos->parent == parent && hash == pos->hash;
kernfs_put(pos);
if (!valid)
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 46b58de..a91d7a1 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -26,7 +26,8 @@ struct kernfs_iattrs {
struct simple_xattrs xattrs;
};
-#define KN_DEACTIVATED_BIAS INT_MIN
+/* +1 to avoid triggering overflow warning when negating it */
+#define KN_DEACTIVATED_BIAS (INT_MIN + 1)
/* KERNFS_TYPE_MASK and types are defined in include/linux/kernfs.h */
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index dc4cd6c..917bc6c 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -38,7 +38,6 @@ enum kernfs_node_type {
#define KERNFS_FLAG_MASK ~KERNFS_TYPE_MASK
enum kernfs_node_flag {
- KERNFS_REMOVED = 0x0010,
KERNFS_NS = 0x0020,
KERNFS_HAS_SEQ_SHOW = 0x0040,
KERNFS_HAS_MMAP = 0x0080,
--
1.8.5.3
--
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