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Commit a9746d8d authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: factor out cgroup_kn_lock_live() and cgroup_kn_unlock() 



cgroup_mkdir(), cgroup_rmdir() and cgroup_subtree_control_write()
share the logic to break active protection so that they can grab
cgroup_tree_mutex which nests above active protection and/or remove
self.  Factor out this logic into cgroup_kn_lock_live() and
cgroup_kn_unlock().

This patch doesn't introduce any functional changes.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent cfc79d5b

kernel/cgroup.c

+90 −67
Original line number Diff line number Diff line
@@ -1093,6 +1093,75 @@ static void cgroup_put(struct cgroup *cgrp) 
	call_rcu(&cgrp->rcu_head, cgroup_free_rcu);

}



/**

 * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods

 * @kn: the kernfs_node being serviced

 *

 * This helper undoes cgroup_kn_lock_live() and should be invoked before

 * the method finishes if locking succeeded.  Note that once this function

 * returns the cgroup returned by cgroup_kn_lock_live() may become

 * inaccessible any time.  If the caller intends to continue to access the

 * cgroup, it should pin it before invoking this function.

 */

static void cgroup_kn_unlock(struct kernfs_node *kn)

{

	struct cgroup *cgrp;



	if (kernfs_type(kn) == KERNFS_DIR)

		cgrp = kn->priv;

	else

		cgrp = kn->parent->priv;



	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&cgroup_tree_mutex);



	kernfs_unbreak_active_protection(kn);

	cgroup_put(cgrp);

}



/**

 * cgroup_kn_lock_live - locking helper for cgroup kernfs methods

 * @kn: the kernfs_node being serviced

 *

 * This helper is to be used by a cgroup kernfs method currently servicing

 * @kn.  It breaks the active protection, performs cgroup locking and

 * verifies that the associated cgroup is alive.  Returns the cgroup if

 * alive; otherwise, %NULL.  A successful return should be undone by a

 * matching cgroup_kn_unlock() invocation.

 *

 * Any cgroup kernfs method implementation which requires locking the

 * associated cgroup should use this helper.  It avoids nesting cgroup

 * locking under kernfs active protection and allows all kernfs operations

 * including self-removal.

 */

static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn)

{

	struct cgroup *cgrp;



	if (kernfs_type(kn) == KERNFS_DIR)

		cgrp = kn->priv;

	else

		cgrp = kn->parent->priv;



	/*

	 * We're gonna grab cgroup_tree_mutex which nests outside kernfs

	 * active_ref.  cgroup liveliness check alone provides enough

	 * protection against removal.  Ensure @cgrp stays accessible and

	 * break the active_ref protection.

	 */

	cgroup_get(cgrp);

	kernfs_break_active_protection(kn);



	mutex_lock(&cgroup_tree_mutex);

	mutex_lock(&cgroup_mutex);



	if (!cgroup_is_dead(cgrp))

		return cgrp;



	cgroup_kn_unlock(kn);

	return NULL;

}



static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)

{

	char name[CGROUP_FILE_NAME_MAX];
@@ -2541,7 +2610,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of, 
					    loff_t off)

{

	unsigned int enable = 0, disable = 0;

	struct cgroup *cgrp = of_css(of)->cgroup, *child;

	struct cgroup *cgrp, *child;

	struct cgroup_subsys *ss;

	char *tok;

	int ssid, ret;
@@ -2573,20 +2642,9 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of, 
			return -EINVAL;

	}



	/*

	 * We're gonna grab cgroup_tree_mutex which nests outside kernfs

	 * active_ref.  cgroup_lock_live_group() already provides enough

	 * protection.  Ensure @cgrp stays accessible and break the

	 * active_ref protection.

	 */

	cgroup_get(cgrp);

	kernfs_break_active_protection(of->kn);



	mutex_lock(&cgroup_tree_mutex);

	if (!cgroup_lock_live_group(cgrp)) {

		ret = -ENODEV;

		goto out_unlock_tree;

	}

	cgrp = cgroup_kn_lock_live(of->kn);

	if (!cgrp)

		return -ENODEV;



	for_each_subsys(ss, ssid) {

		if (enable & (1 << ssid)) {
@@ -2610,14 +2668,12 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of, 
				cgroup_get(child);

				prepare_to_wait(&child->offline_waitq, &wait,

						TASK_UNINTERRUPTIBLE);

				mutex_unlock(&cgroup_mutex);

				mutex_unlock(&cgroup_tree_mutex);

				cgroup_kn_unlock(of->kn);

				schedule();

				finish_wait(&child->offline_waitq, &wait);

				cgroup_put(child);



				ret = restart_syscall();

				goto out_unbreak;

				return restart_syscall();

			}



			/* unavailable or not enabled on the parent? */
@@ -2693,12 +2749,7 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of, 
	kernfs_activate(cgrp->kn);

	ret = 0;

out_unlock:

	mutex_unlock(&cgroup_mutex);

out_unlock_tree:

	mutex_unlock(&cgroup_tree_mutex);

out_unbreak:

	kernfs_unbreak_active_protection(of->kn);

	cgroup_put(cgrp);

	cgroup_kn_unlock(of->kn);

	return ret ?: nbytes;



err_undo_css:
@@ -4238,25 +4289,16 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss) 
static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,

			umode_t mode)

{

	struct cgroup *parent = parent_kn->priv, *cgrp;

	struct cgroup_root *root = parent->root;

	struct cgroup *parent, *cgrp;

	struct cgroup_root *root;

	struct cgroup_subsys *ss;

	struct kernfs_node *kn;

	int ssid, ret;



	/*

	 * cgroup_mkdir() grabs cgroup_tree_mutex which nests outside

	 * kernfs active_ref and cgroup_create() already synchronizes

	 * properly against removal through cgroup_lock_live_group().

	 * Break it before calling cgroup_create().

	 */

	cgroup_get(parent);

	kernfs_break_active_protection(parent_kn);

	mutex_lock(&cgroup_tree_mutex);

	if (!cgroup_lock_live_group(parent)) {

		ret = -ENODEV;

		goto out_unlock_tree;

	}

	parent = cgroup_kn_lock_live(parent_kn);

	if (!parent)

		return -ENODEV;

	root = parent->root;



	/* allocate the cgroup and its ID, 0 is reserved for the root */

	cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
@@ -4348,11 +4390,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, 
out_free_cgrp:

	kfree(cgrp);

out_unlock:

	mutex_unlock(&cgroup_mutex);

out_unlock_tree:

	mutex_unlock(&cgroup_tree_mutex);

	kernfs_unbreak_active_protection(parent_kn);

	cgroup_put(parent);

	cgroup_kn_unlock(parent_kn);

	return ret;



out_destroy:
@@ -4579,32 +4617,17 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp) 


static int cgroup_rmdir(struct kernfs_node *kn)

{

	struct cgroup *cgrp = kn->priv;

	struct cgroup *cgrp;

	int ret = 0;



	/*

	 * This is self-destruction but @kn can't be removed while this

	 * callback is in progress.  Let's break active protection.  Once

	 * the protection is broken, @cgrp can be destroyed at any point.

	 * Pin it so that it stays accessible.

	 */

	cgroup_get(cgrp);

	kernfs_break_active_protection(kn);



	mutex_lock(&cgroup_tree_mutex);

	mutex_lock(&cgroup_mutex);

	cgrp = cgroup_kn_lock_live(kn);

	if (!cgrp)

		return 0;

	cgroup_get(cgrp);	/* for @kn->priv clearing */



	/*

	 * @cgrp might already have been destroyed while we're trying to

	 * grab the mutexes.

	 */

	if (!cgroup_is_dead(cgrp))

	ret = cgroup_destroy_locked(cgrp);



	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&cgroup_tree_mutex);



	kernfs_unbreak_active_protection(kn);

	cgroup_kn_unlock(kn);



	/*

	 * There are two control paths which try to determine cgroup from