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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@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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182fd64b66
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81c173cb5e
@ -22,6 +22,12 @@ DEFINE_MUTEX(kernfs_mutex);
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#define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
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static bool kernfs_active(struct kernfs_node *kn)
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{
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lockdep_assert_held(&kernfs_mutex);
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return atomic_read(&kn->active) >= 0;
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}
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static bool kernfs_lockdep(struct kernfs_node *kn)
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{
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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@ -183,25 +189,20 @@ void kernfs_put_active(struct kernfs_node *kn)
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}
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/**
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* kernfs_deactivate - deactivate kernfs_node
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* @kn: kernfs_node to deactivate
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* kernfs_drain - drain kernfs_node
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* @kn: kernfs_node to drain
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*
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* Deny new active references, drain existing ones and nuke all
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* existing mmaps. Mutiple removers may invoke this function
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* concurrently on @kn and all will return after deactivation and
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* draining are complete.
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* Drain existing usages and nuke all existing mmaps of @kn. Mutiple
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* removers may invoke this function concurrently on @kn and all will
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* return after draining is complete.
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*/
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static void kernfs_deactivate(struct kernfs_node *kn)
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static void kernfs_drain(struct kernfs_node *kn)
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__releases(&kernfs_mutex) __acquires(&kernfs_mutex)
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{
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struct kernfs_root *root = kernfs_root(kn);
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lockdep_assert_held(&kernfs_mutex);
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BUG_ON(!(kn->flags & KERNFS_REMOVED));
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/* only the first invocation on @kn should deactivate it */
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if (atomic_read(&kn->active) >= 0)
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atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
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WARN_ON_ONCE(kernfs_active(kn));
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mutex_unlock(&kernfs_mutex);
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@ -253,13 +254,15 @@ void kernfs_put(struct kernfs_node *kn)
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return;
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root = kernfs_root(kn);
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repeat:
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/* Moving/renaming is always done while holding reference.
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/*
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* Moving/renaming is always done while holding reference.
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* kn->parent won't change beneath us.
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*/
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parent = kn->parent;
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WARN(!(kn->flags & KERNFS_REMOVED), "kernfs: free using entry: %s/%s\n",
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parent ? parent->name : "", kn->name);
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WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,
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"kernfs_put: %s/%s: released with incorrect active_ref %d\n",
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parent ? parent->name : "", kn->name, atomic_read(&kn->active));
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if (kernfs_type(kn) == KERNFS_LINK)
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kernfs_put(kn->symlink.target_kn);
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@ -301,8 +304,8 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
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kn = dentry->d_fsdata;
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mutex_lock(&kernfs_mutex);
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/* The kernfs node has been deleted */
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if (kn->flags & KERNFS_REMOVED)
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/* The kernfs node has been deactivated */
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if (!kernfs_active(kn))
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goto out_bad;
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/* The kernfs node has been moved? */
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@ -371,12 +374,12 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
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kn->ino = ret;
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atomic_set(&kn->count, 1);
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atomic_set(&kn->active, 0);
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atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
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RB_CLEAR_NODE(&kn->rb);
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kn->name = name;
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kn->mode = mode;
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kn->flags = flags | KERNFS_REMOVED;
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kn->flags = flags;
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return kn;
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@ -432,7 +435,7 @@ int kernfs_add_one(struct kernfs_node *kn)
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goto out_unlock;
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ret = -ENOENT;
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if (parent->flags & KERNFS_REMOVED)
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if (!kernfs_active(parent))
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goto out_unlock;
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kn->hash = kernfs_name_hash(kn->name, kn->ns);
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@ -449,7 +452,7 @@ int kernfs_add_one(struct kernfs_node *kn)
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}
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/* Mark the entry added into directory tree */
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kn->flags &= ~KERNFS_REMOVED;
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atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
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ret = 0;
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out_unlock:
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mutex_unlock(&kernfs_mutex);
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@ -549,7 +552,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
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return ERR_PTR(-ENOMEM);
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}
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kn->flags &= ~KERNFS_REMOVED;
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atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
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kn->priv = priv;
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kn->dir.root = root;
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@ -763,24 +766,25 @@ static void __kernfs_remove(struct kernfs_node *kn)
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pr_debug("kernfs %s: removing\n", kn->name);
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/* disable lookup and node creation under @kn */
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/* prevent any new usage under @kn by deactivating all nodes */
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pos = NULL;
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while ((pos = kernfs_next_descendant_post(pos, kn)))
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pos->flags |= KERNFS_REMOVED;
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if (kernfs_active(pos))
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atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
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/* deactivate and unlink the subtree node-by-node */
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do {
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pos = kernfs_leftmost_descendant(kn);
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/*
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* kernfs_deactivate() drops kernfs_mutex temporarily and
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* @pos's base ref could have been put by someone else by
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* the time the function returns. Make sure it doesn't go
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* away underneath us.
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* kernfs_drain() drops kernfs_mutex temporarily and @pos's
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* base ref could have been put by someone else by the time
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* the function returns. Make sure it doesn't go away
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* underneath us.
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*/
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kernfs_get(pos);
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kernfs_deactivate(pos);
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kernfs_drain(pos);
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/*
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* kernfs_unlink_sibling() succeeds once per node. Use it
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@ -865,7 +869,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
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mutex_lock(&kernfs_mutex);
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error = -ENOENT;
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if ((kn->flags | new_parent->flags) & KERNFS_REMOVED)
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if (!kernfs_active(kn) || !kernfs_active(new_parent))
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goto out;
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error = 0;
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@ -925,7 +929,7 @@ static struct kernfs_node *kernfs_dir_pos(const void *ns,
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struct kernfs_node *parent, loff_t hash, struct kernfs_node *pos)
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{
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if (pos) {
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int valid = !(pos->flags & KERNFS_REMOVED) &&
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int valid = kernfs_active(pos) &&
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pos->parent == parent && hash == pos->hash;
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kernfs_put(pos);
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if (!valid)
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@ -26,7 +26,8 @@ struct kernfs_iattrs {
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struct simple_xattrs xattrs;
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};
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#define KN_DEACTIVATED_BIAS INT_MIN
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/* +1 to avoid triggering overflow warning when negating it */
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#define KN_DEACTIVATED_BIAS (INT_MIN + 1)
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/* KERNFS_TYPE_MASK and types are defined in include/linux/kernfs.h */
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@ -38,7 +38,6 @@ enum kernfs_node_type {
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#define KERNFS_FLAG_MASK ~KERNFS_TYPE_MASK
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enum kernfs_node_flag {
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KERNFS_REMOVED = 0x0010,
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KERNFS_NS = 0x0020,
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KERNFS_HAS_SEQ_SHOW = 0x0040,
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KERNFS_HAS_MMAP = 0x0080,
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