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Commit 81c173cb authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman
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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: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 182fd64b

fs/kernfs/dir.c

+35 −31
Original line number Diff line number Diff line
@@ -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)

fs/kernfs/kernfs-internal.h

+2 −1
Original line number Diff line number Diff line
@@ -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 */

include/linux/kernfs.h

+0 −1
Original line number Diff line number Diff line
@@ -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,