Commit 63348894 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Greg Kroah-Hartman
Browse files

kernfs: Use RCU to access kernfs_node::parent. 



kernfs_rename_lock is used to obtain stable kernfs_node::{name|parent}
pointer. This is a preparation to access kernfs_node::parent under RCU
and ensure that the pointer remains stable under the RCU lifetime
guarantees.

For a complete path, as it is done in kernfs_path_from_node(), the
kernfs_rename_lock is still required in order to obtain a stable parent
relationship while computing the relevant node depth. This must not
change while the nodes are inspected in order to build the path.
If the kernfs user never moves the nodes (changes the parent) then the
kernfs_rename_lock is not required and the RCU guarantees are
sufficient. This "restriction" can be set with
KERNFS_ROOT_INVARIANT_PARENT. Otherwise the lock is required.

Rename kernfs_node::parent to kernfs_node::__parent to denote the RCU
access and use RCU accessor while accessing the node.
Make cgroup use KERNFS_ROOT_INVARIANT_PARENT since the parent here can
not change.

Acked-by: default avatarTejun Heo <tj@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20250213145023.2820193-6-bigeasy@linutronix.de


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 9aab10a0

arch/x86/kernel/cpu/resctrl/rdtgroup.c

+44 −21
Original line number Diff line number Diff line
@@ -956,10 +956,20 @@ static int rdt_last_cmd_status_show(struct kernfs_open_file *of, 
	return 0;

}



static void *rdt_kn_parent_priv(struct kernfs_node *kn)

{

	/*

	 * The parent pointer is only valid within RCU section since it can be

	 * replaced.

	 */

	guard(rcu)();

	return rcu_dereference(kn->__parent)->priv;

}



static int rdt_num_closids_show(struct kernfs_open_file *of,

				struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);



	seq_printf(seq, "%u\n", s->num_closid);

	return 0;
@@ -968,7 +978,7 @@ static int rdt_num_closids_show(struct kernfs_open_file *of, 
static int rdt_default_ctrl_show(struct kernfs_open_file *of,

			     struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	seq_printf(seq, "%x\n", r->default_ctrl);
@@ -978,7 +988,7 @@ static int rdt_default_ctrl_show(struct kernfs_open_file *of, 
static int rdt_min_cbm_bits_show(struct kernfs_open_file *of,

			     struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	seq_printf(seq, "%u\n", r->cache.min_cbm_bits);
@@ -988,7 +998,7 @@ static int rdt_min_cbm_bits_show(struct kernfs_open_file *of, 
static int rdt_shareable_bits_show(struct kernfs_open_file *of,

				   struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	seq_printf(seq, "%x\n", r->cache.shareable_bits);
@@ -1012,7 +1022,7 @@ static int rdt_shareable_bits_show(struct kernfs_open_file *of, 
static int rdt_bit_usage_show(struct kernfs_open_file *of,

			      struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	/*

	 * Use unsigned long even though only 32 bits are used to ensure

	 * test_bit() is used safely.
@@ -1094,7 +1104,7 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of, 
static int rdt_min_bw_show(struct kernfs_open_file *of,

			     struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	seq_printf(seq, "%u\n", r->membw.min_bw);
@@ -1104,7 +1114,7 @@ static int rdt_min_bw_show(struct kernfs_open_file *of, 
static int rdt_num_rmids_show(struct kernfs_open_file *of,

			      struct seq_file *seq, void *v)

{

	struct rdt_resource *r = of->kn->parent->priv;

	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);



	seq_printf(seq, "%d\n", r->num_rmid);
@@ -1114,7 +1124,7 @@ static int rdt_num_rmids_show(struct kernfs_open_file *of, 
static int rdt_mon_features_show(struct kernfs_open_file *of,

				 struct seq_file *seq, void *v)

{

	struct rdt_resource *r = of->kn->parent->priv;

	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);

	struct mon_evt *mevt;



	list_for_each_entry(mevt, &r->evt_list, list) {
@@ -1129,7 +1139,7 @@ static int rdt_mon_features_show(struct kernfs_open_file *of, 
static int rdt_bw_gran_show(struct kernfs_open_file *of,

			     struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	seq_printf(seq, "%u\n", r->membw.bw_gran);
@@ -1139,7 +1149,7 @@ static int rdt_bw_gran_show(struct kernfs_open_file *of, 
static int rdt_delay_linear_show(struct kernfs_open_file *of,

			     struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	seq_printf(seq, "%u\n", r->membw.delay_linear);
@@ -1157,7 +1167,7 @@ static int max_threshold_occ_show(struct kernfs_open_file *of, 
static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of,

					 struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	if (r->membw.throttle_mode == THREAD_THROTTLE_PER_THREAD)
@@ -1222,7 +1232,7 @@ static enum resctrl_conf_type resctrl_peer_type(enum resctrl_conf_type my_type) 
static int rdt_has_sparse_bitmasks_show(struct kernfs_open_file *of,

					struct seq_file *seq, void *v)

{

	struct resctrl_schema *s = of->kn->parent->priv;

	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);

	struct rdt_resource *r = s->res;



	seq_printf(seq, "%u\n", r->cache.arch_has_sparse_bitmasks);
@@ -1634,7 +1644,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid 
static int mbm_total_bytes_config_show(struct kernfs_open_file *of,

				       struct seq_file *seq, void *v)

{

	struct rdt_resource *r = of->kn->parent->priv;

	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);



	mbm_config_show(seq, r, QOS_L3_MBM_TOTAL_EVENT_ID);
@@ -1644,7 +1654,7 @@ static int mbm_total_bytes_config_show(struct kernfs_open_file *of, 
static int mbm_local_bytes_config_show(struct kernfs_open_file *of,

				       struct seq_file *seq, void *v)

{

	struct rdt_resource *r = of->kn->parent->priv;

	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);



	mbm_config_show(seq, r, QOS_L3_MBM_LOCAL_EVENT_ID);
@@ -1750,7 +1760,7 @@ static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of, 
					    char *buf, size_t nbytes,

					    loff_t off)

{

	struct rdt_resource *r = of->kn->parent->priv;

	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);

	int ret;



	/* Valid input requires a trailing newline */
@@ -1776,7 +1786,7 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of, 
					    char *buf, size_t nbytes,

					    loff_t off)

{

	struct rdt_resource *r = of->kn->parent->priv;

	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);

	int ret;



	/* Valid input requires a trailing newline */
@@ -2440,12 +2450,13 @@ static struct rdtgroup *kernfs_to_rdtgroup(struct kernfs_node *kn) 
		 * resource. "info" and its subdirectories don't

		 * have rdtgroup structures, so return NULL here.

		 */

		if (kn == kn_info || kn->parent == kn_info)

		if (kn == kn_info ||

		    rcu_access_pointer(kn->__parent) == kn_info)

			return NULL;

		else

			return kn->priv;

	} else {

		return kn->parent->priv;

		return rdt_kn_parent_priv(kn);

	}

}
@@ -3771,9 +3782,18 @@ static int rdtgroup_rmdir_ctrl(struct rdtgroup *rdtgrp, cpumask_var_t tmpmask) 
	return 0;

}



static struct kernfs_node *rdt_kn_parent(struct kernfs_node *kn)

{

	/*

	 * Valid within the RCU section it was obtained or while rdtgroup_mutex

	 * is held.

	 */

	return rcu_dereference_check(kn->__parent, lockdep_is_held(&rdtgroup_mutex));

}



static int rdtgroup_rmdir(struct kernfs_node *kn)

{

	struct kernfs_node *parent_kn = kn->parent;

	struct kernfs_node *parent_kn;

	struct rdtgroup *rdtgrp;

	cpumask_var_t tmpmask;

	int ret = 0;
@@ -3786,6 +3806,7 @@ static int rdtgroup_rmdir(struct kernfs_node *kn) 
		ret = -EPERM;

		goto out;

	}

	parent_kn = rdt_kn_parent(kn);



	/*

	 * If the rdtgroup is a ctrl_mon group and parent directory
@@ -3854,6 +3875,7 @@ static void mongrp_reparent(struct rdtgroup *rdtgrp, 
static int rdtgroup_rename(struct kernfs_node *kn,

			   struct kernfs_node *new_parent, const char *new_name)

{

	struct kernfs_node *kn_parent;

	struct rdtgroup *new_prdtgrp;

	struct rdtgroup *rdtgrp;

	cpumask_var_t tmpmask;
@@ -3888,8 +3910,9 @@ static int rdtgroup_rename(struct kernfs_node *kn, 
		goto out;

	}



	if (rdtgrp->type != RDTMON_GROUP || !kn->parent ||

	    !is_mon_groups(kn->parent, kn->name)) {

	kn_parent = rdt_kn_parent(kn);

	if (rdtgrp->type != RDTMON_GROUP || !kn_parent ||

	    !is_mon_groups(kn_parent, kn->name)) {

		rdt_last_cmd_puts("Source must be a MON group\n");

		ret = -EPERM;

		goto out;

fs/kernfs/dir.c

+60 −36
Original line number Diff line number Diff line
@@ -17,7 +17,7 @@ 


#include "kernfs-internal.h"



static DEFINE_RWLOCK(kernfs_rename_lock);	/* kn->parent and ->name */

DEFINE_RWLOCK(kernfs_rename_lock);	/* kn->parent and ->name */

/*

 * Don't use rename_lock to piggy back on pr_cont_buf. We don't want to

 * call pr_cont() while holding rename_lock. Because sometimes pr_cont()
@@ -56,7 +56,7 @@ static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen) 
	if (!kn)

		return strscpy(buf, "(null)", buflen);



	return strscpy(buf, kn->parent ? kn->name : "/", buflen);

	return strscpy(buf, rcu_access_pointer(kn->__parent) ? kn->name : "/", buflen);

}



/* kernfs_node_depth - compute depth from @from to @to */
@@ -64,9 +64,9 @@ static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to) 
{

	size_t depth = 0;



	while (to->parent && to != from) {

	while (rcu_dereference(to->__parent) && to != from) {

		depth++;

		to = to->parent;

		to = rcu_dereference(to->__parent);

	}

	return depth;

}
@@ -84,18 +84,18 @@ static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a, 
	db = kernfs_depth(rb->kn, b);



	while (da > db) {

		a = a->parent;

		a = rcu_dereference(a->__parent);

		da--;

	}

	while (db > da) {

		b = b->parent;

		b = rcu_dereference(b->__parent);

		db--;

	}



	/* worst case b and a will be the same at root */

	while (b != a) {

		b = b->parent;

		a = a->parent;

		b = rcu_dereference(b->__parent);

		a = rcu_dereference(a->__parent);

	}



	return a;
@@ -168,8 +168,9 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, 


	/* Calculate how many bytes we need for the rest */

	for (i = depth_to - 1; i >= 0; i--) {



		for (kn = kn_to, j = 0; j < i; j++)

			kn = kn->parent;

			kn = rcu_dereference(kn->__parent);



		len += scnprintf(buf + len, buflen - len, "/%s", kn->name);

	}
@@ -226,6 +227,7 @@ int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from, 
	unsigned long flags;

	int ret;



	guard(rcu)();

	read_lock_irqsave(&kernfs_rename_lock, flags);

	ret = kernfs_path_from_node_locked(to, from, buf, buflen);

	read_unlock_irqrestore(&kernfs_rename_lock, flags);
@@ -295,7 +297,7 @@ struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn) 
	unsigned long flags;



	read_lock_irqsave(&kernfs_rename_lock, flags);

	parent = kn->parent;

	parent = kernfs_parent(kn);

	kernfs_get(parent);

	read_unlock_irqrestore(&kernfs_rename_lock, flags);
@@ -360,8 +362,12 @@ static int kernfs_sd_compare(const struct kernfs_node *left, 
 */

static int kernfs_link_sibling(struct kernfs_node *kn)

{

	struct rb_node **node = &kn->parent->dir.children.rb_node;

	struct rb_node *parent = NULL;

	struct kernfs_node *kn_parent;

	struct rb_node **node;



	kn_parent = kernfs_parent(kn);

	node = &kn_parent->dir.children.rb_node;



	while (*node) {

		struct kernfs_node *pos;
@@ -380,13 +386,13 @@ static int kernfs_link_sibling(struct kernfs_node *kn) 


	/* add new node and rebalance the tree */

	rb_link_node(&kn->rb, parent, node);

	rb_insert_color(&kn->rb, &kn->parent->dir.children);

	rb_insert_color(&kn->rb, &kn_parent->dir.children);



	/* successfully added, account subdir number */

	down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);

	if (kernfs_type(kn) == KERNFS_DIR)

		kn->parent->dir.subdirs++;

	kernfs_inc_rev(kn->parent);

		kn_parent->dir.subdirs++;

	kernfs_inc_rev(kn_parent);

	up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);



	return 0;
@@ -407,16 +413,19 @@ static int kernfs_link_sibling(struct kernfs_node *kn) 
 */

static bool kernfs_unlink_sibling(struct kernfs_node *kn)

{

	struct kernfs_node *kn_parent;



	if (RB_EMPTY_NODE(&kn->rb))

		return false;



	kn_parent = kernfs_parent(kn);

	down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);

	if (kernfs_type(kn) == KERNFS_DIR)

		kn->parent->dir.subdirs--;

	kernfs_inc_rev(kn->parent);

		kn_parent->dir.subdirs--;

	kernfs_inc_rev(kn_parent);

	up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);



	rb_erase(&kn->rb, &kn->parent->dir.children);

	rb_erase(&kn->rb, &kn_parent->dir.children);

	RB_CLEAR_NODE(&kn->rb);

	return true;

}
@@ -562,7 +571,7 @@ void kernfs_put(struct kernfs_node *kn) 
	 * Moving/renaming is always done while holding reference.

	 * kn->parent won't change beneath us.

	 */

	parent = kn->parent;

	parent = kernfs_parent(kn);



	WARN_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS,

		  "kernfs_put: %s/%s: released with incorrect active_ref %d\n",
@@ -701,7 +710,7 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent, 
			       name, mode, uid, gid, flags);

	if (kn) {

		kernfs_get(parent);

		kn->parent = parent;

		rcu_assign_pointer(kn->__parent, parent);

	}

	return kn;

}
@@ -769,13 +778,14 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root, 
 */

int kernfs_add_one(struct kernfs_node *kn)

{

	struct kernfs_node *parent = kn->parent;

	struct kernfs_root *root = kernfs_root(parent);

	struct kernfs_root *root = kernfs_root(kn);

	struct kernfs_iattrs *ps_iattr;

	struct kernfs_node *parent;

	bool has_ns;

	int ret;



	down_write(&root->kernfs_rwsem);

	parent = kernfs_parent(kn);



	ret = -EINVAL;

	has_ns = kernfs_ns_enabled(parent);
@@ -949,6 +959,11 @@ struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent, 
	return kn;

}



unsigned int kernfs_root_flags(struct kernfs_node *kn)

{

	return kernfs_root(kn)->flags;

}



/**

 * kernfs_create_root - create a new kernfs hierarchy

 * @scops: optional syscall operations for the hierarchy
@@ -1112,7 +1127,7 @@ struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent, 
static int kernfs_dop_revalidate(struct inode *dir, const struct qstr *name,

				 struct dentry *dentry, unsigned int flags)

{

	struct kernfs_node *kn;

	struct kernfs_node *kn, *parent;

	struct kernfs_root *root;



	if (flags & LOOKUP_RCU)
@@ -1163,8 +1178,9 @@ static int kernfs_dop_revalidate(struct inode *dir, const struct qstr *name, 
	if (!kernfs_active(kn))

		goto out_bad;



	parent = kernfs_parent(kn);

	/* The kernfs node has been moved? */

	if (kernfs_dentry_node(dentry->d_parent) != kn->parent)

	if (kernfs_dentry_node(dentry->d_parent) != parent)

		goto out_bad;



	/* The kernfs node has been renamed */
@@ -1172,7 +1188,7 @@ static int kernfs_dop_revalidate(struct inode *dir, const struct qstr *name, 
		goto out_bad;



	/* The kernfs node has been moved to a different namespace */

	if (kn->parent && kernfs_ns_enabled(kn->parent) &&

	if (parent && kernfs_ns_enabled(parent) &&

	    kernfs_info(dentry->d_sb)->ns != kn->ns)

		goto out_bad;
@@ -1365,7 +1381,7 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos, 
		return kernfs_leftmost_descendant(rb_to_kn(rbn));



	/* no sibling left, visit parent */

	return pos->parent;

	return kernfs_parent(pos);

}



static void kernfs_activate_one(struct kernfs_node *kn)
@@ -1377,7 +1393,7 @@ static void kernfs_activate_one(struct kernfs_node *kn) 
	if (kernfs_active(kn) || (kn->flags & (KERNFS_HIDDEN | KERNFS_REMOVING)))

		return;



	WARN_ON_ONCE(kn->parent && RB_EMPTY_NODE(&kn->rb));

	WARN_ON_ONCE(rcu_access_pointer(kn->__parent) && RB_EMPTY_NODE(&kn->rb));

	WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);



	atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
@@ -1447,7 +1463,7 @@ void kernfs_show(struct kernfs_node *kn, bool show) 


static void __kernfs_remove(struct kernfs_node *kn)

{

	struct kernfs_node *pos;

	struct kernfs_node *pos, *parent;



	/* Short-circuit if non-root @kn has already finished removal. */

	if (!kn)
@@ -1459,7 +1475,7 @@ static void __kernfs_remove(struct kernfs_node *kn) 
	 * This is for kernfs_remove_self() which plays with active ref

	 * after removal.

	 */

	if (kn->parent && RB_EMPTY_NODE(&kn->rb))

	if (kernfs_parent(kn) && RB_EMPTY_NODE(&kn->rb))

		return;



	pr_debug("kernfs %s: removing\n", kn->name);
@@ -1485,14 +1501,14 @@ static void __kernfs_remove(struct kernfs_node *kn) 
		kernfs_get(pos);



		kernfs_drain(pos);



		parent = kernfs_parent(pos);

		/*

		 * kernfs_unlink_sibling() succeeds once per node.  Use it

		 * to decide who's responsible for cleanups.

		 */

		if (!pos->parent || kernfs_unlink_sibling(pos)) {

		if (!parent || kernfs_unlink_sibling(pos)) {

			struct kernfs_iattrs *ps_iattr =

				pos->parent ? pos->parent->iattr : NULL;

				parent ? parent->iattr : NULL;



			/* update timestamps on the parent */

			down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
@@ -1722,7 +1738,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent, 
	int error;



	/* can't move or rename root */

	if (!kn->parent)

	if (!rcu_access_pointer(kn->__parent))

		return -EINVAL;



	root = kernfs_root(kn);
@@ -1733,8 +1749,15 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent, 
	    (new_parent->flags & KERNFS_EMPTY_DIR))

		goto out;



	old_parent = kernfs_parent(kn);

	if (root->flags & KERNFS_ROOT_INVARIANT_PARENT) {

		error = -EINVAL;

		if (WARN_ON_ONCE(old_parent != new_parent))

			goto out;

	}



	error = 0;

	if ((kn->parent == new_parent) && (kn->ns == new_ns) &&

	if ((old_parent == new_parent) && (kn->ns == new_ns) &&

	    (strcmp(kn->name, new_name) == 0))

		goto out;	/* nothing to rename */
@@ -1761,8 +1784,8 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent, 
	/* rename_lock protects ->parent and ->name accessors */

	write_lock_irq(&kernfs_rename_lock);



	old_parent = kn->parent;

	kn->parent = new_parent;

	old_parent = kernfs_parent(kn);

	rcu_assign_pointer(kn->__parent, new_parent);



	kn->ns = new_ns;

	if (new_name) {
@@ -1795,7 +1818,8 @@ static struct kernfs_node *kernfs_dir_pos(const void *ns, 
{

	if (pos) {

		int valid = kernfs_active(pos) &&

			pos->parent == parent && hash == pos->hash;

			rcu_access_pointer(pos->__parent) == parent &&

			hash == pos->hash;

		kernfs_put(pos);

		if (!valid)

			pos = NULL;

fs/kernfs/kernfs-internal.h

+29 −3
Original line number Diff line number Diff line
@@ -19,6 +19,8 @@ 
#include <linux/kernfs.h>

#include <linux/fs_context.h>



extern rwlock_t kernfs_rename_lock;



struct kernfs_iattrs {

	kuid_t			ia_uid;

	kgid_t			ia_gid;
@@ -64,11 +66,14 @@ struct kernfs_root { 
 *

 * Return: the kernfs_root @kn belongs to.

 */

static inline struct kernfs_root *kernfs_root(struct kernfs_node *kn)

static inline struct kernfs_root *kernfs_root(const struct kernfs_node *kn)

{

	const struct kernfs_node *knp;

	/* if parent exists, it's always a dir; otherwise, @sd is a dir */

	if (kn->parent)

		kn = kn->parent;

	guard(rcu)();

	knp = rcu_dereference(kn->__parent);

	if (knp)

		kn = knp;

	return kn->dir.root;

}
@@ -97,6 +102,27 @@ struct kernfs_super_info { 
};

#define kernfs_info(SB) ((struct kernfs_super_info *)(SB->s_fs_info))



static inline bool kernfs_root_is_locked(const struct kernfs_node *kn)

{

	return lockdep_is_held(&kernfs_root(kn)->kernfs_rwsem);

}



static inline struct kernfs_node *kernfs_parent(const struct kernfs_node *kn)

{

	/*

	 * The kernfs_node::__parent remains valid within a RCU section. The kn

	 * can be reparented (and renamed) which changes the entry. This can be

	 * avoided by locking kernfs_root::kernfs_rwsem or kernfs_rename_lock.

	 * Both locks can be used to obtain a reference on __parent. Once the

	 * reference count reaches 0 then the node is about to be freed

	 * and can not be renamed (or become a different parent) anymore.

	 */

	return rcu_dereference_check(kn->__parent,

				     kernfs_root_is_locked(kn) ||

				     lockdep_is_held(&kernfs_rename_lock) ||

				     !atomic_read(&kn->count));

}



static inline struct kernfs_node *kernfs_dentry_node(struct dentry *dentry)

{

	if (d_really_is_negative(dentry))

fs/kernfs/mount.c

+5 −5
Original line number Diff line number Diff line
@@ -148,7 +148,7 @@ static struct dentry *kernfs_get_parent_dentry(struct dentry *child) 
	struct kernfs_root *root = kernfs_root(kn);



	guard(rwsem_read)(&root->kernfs_rwsem);

	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));

	return d_obtain_alias(kernfs_get_inode(child->d_sb, kernfs_parent(kn)));

}



static const struct export_operations kernfs_export_ops = {
@@ -188,10 +188,10 @@ static struct kernfs_node *find_next_ancestor(struct kernfs_node *child, 
		return NULL;

	}



	while (child->parent != parent) {

		if (!child->parent)

	while (kernfs_parent(child) != parent) {

		child = kernfs_parent(child);

		if (!child)

			return NULL;

		child = child->parent;

	}



	return child;
@@ -216,7 +216,7 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn, 
	dentry = dget(sb->s_root);



	/* Check if this is the root kernfs_node */

	if (!kn->parent)

	if (!rcu_access_pointer(kn->__parent))

		return dentry;



	root = kernfs_root(kn);

fs/kernfs/symlink.c

+12 −11
Original line number Diff line number Diff line
@@ -62,10 +62,10 @@ static int kernfs_get_target_path(struct kernfs_node *parent, 


	/* go up to the root, stop at the base */

	base = parent;

	while (base->parent) {

		kn = target->parent;

		while (kn->parent && base != kn)

			kn = kn->parent;

	while (kernfs_parent(base)) {

		kn = kernfs_parent(target);

		while (kernfs_parent(kn) && base != kn)

			kn = kernfs_parent(kn);



		if (base == kn)

			break;
@@ -75,14 +75,14 @@ static int kernfs_get_target_path(struct kernfs_node *parent, 


		strcpy(s, "../");

		s += 3;

		base = base->parent;

		base = kernfs_parent(base);

	}



	/* determine end of target string for reverse fillup */

	kn = target;

	while (kn->parent && kn != base) {

	while (kernfs_parent(kn) && kn != base) {

		len += strlen(kn->name) + 1;

		kn = kn->parent;

		kn = kernfs_parent(kn);

	}



	/* check limits */
@@ -94,7 +94,7 @@ static int kernfs_get_target_path(struct kernfs_node *parent, 


	/* reverse fillup of target string from target to base */

	kn = target;

	while (kn->parent && kn != base) {

	while (kernfs_parent(kn) && kn != base) {

		int slen = strlen(kn->name);



		len -= slen;
@@ -102,7 +102,7 @@ static int kernfs_get_target_path(struct kernfs_node *parent, 
		if (len)

			s[--len] = '/';



		kn = kn->parent;

		kn = kernfs_parent(kn);

	}



	return 0;
@@ -111,12 +111,13 @@ static int kernfs_get_target_path(struct kernfs_node *parent, 
static int kernfs_getlink(struct inode *inode, char *path)

{

	struct kernfs_node *kn = inode->i_private;

	struct kernfs_node *parent = kn->parent;

	struct kernfs_node *parent;

	struct kernfs_node *target = kn->symlink.target_kn;

	struct kernfs_root *root = kernfs_root(parent);

	struct kernfs_root *root = kernfs_root(kn);

	int error;



	down_read(&root->kernfs_rwsem);

	parent = kernfs_parent(kn);

	error = kernfs_get_target_path(parent, target, path);

	up_read(&root->kernfs_rwsem);