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Commit 01f6474c authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: nest kernfs active protection under cgroup_mutex 



After the recent cgroup_kn_lock_live() changes, cgroup_mutex is no
longer nested below kernfs active protection.  The two don't have any
relationship now.

This patch nests kernfs active protection under cgroup_mutex.  All
cftype operations now require both cgroup_tree_mutex and cgroup_mutex,
temporary cgroup_mutex releases over kernfs operations are removed,
and cgroup_add/rm_cftypes() grab both mutexes.

This makes cgroup_tree_mutex redundant, which will be removed by the
next patch.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent e76ecaee

kernel/cgroup.c

+16 −11
Original line number Diff line number Diff line
@@ -1127,7 +1127,7 @@ static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn) 
		cgrp = kn->parent->priv;



	/*

	 * We're gonna grab cgroup_tree_mutex which nests outside kernfs

	 * We're gonna grab cgroup_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.
@@ -1150,6 +1150,7 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft) 
	char name[CGROUP_FILE_NAME_MAX];



	lockdep_assert_held(&cgroup_tree_mutex);

	lockdep_assert_held(&cgroup_mutex);

	kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));

}
@@ -1216,11 +1217,9 @@ static int rebind_subsystems(struct cgroup_root *dst_root, unsigned int ss_mask) 
	 * Nothing can fail from this point on.  Remove files for the

	 * removed subsystems and rebind each subsystem.

	 */

	mutex_unlock(&cgroup_mutex);

	for_each_subsys(ss, ssid)

		if (ss_mask & (1 << ssid))

			cgroup_clear_dir(&ss->root->cgrp, 1 << ssid);

	mutex_lock(&cgroup_mutex);



	for_each_subsys(ss, ssid) {

		struct cgroup_root *src_root;
@@ -2946,6 +2945,7 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], 
	int ret;



	lockdep_assert_held(&cgroup_tree_mutex);

	lockdep_assert_held(&cgroup_mutex);



	for (cft = cfts; cft->name[0] != '\0'; cft++) {

		/* does cft->flags tell us to skip this file on @cgrp? */
@@ -2981,6 +2981,7 @@ static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add) 
	int ret = 0;



	lockdep_assert_held(&cgroup_tree_mutex);

	lockdep_assert_held(&cgroup_mutex);



	/* add/rm files for all cgroups created before */

	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
@@ -3049,6 +3050,7 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) 
static int cgroup_rm_cftypes_locked(struct cftype *cfts)

{

	lockdep_assert_held(&cgroup_tree_mutex);

	lockdep_assert_held(&cgroup_mutex);



	if (!cfts || !cfts[0].ss)

		return -ENOENT;
@@ -3075,7 +3077,9 @@ int cgroup_rm_cftypes(struct cftype *cfts) 
	int ret;



	mutex_lock(&cgroup_tree_mutex);

	mutex_lock(&cgroup_mutex);

	ret = cgroup_rm_cftypes_locked(cfts);

	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&cgroup_tree_mutex);

	return ret;

}
@@ -3106,12 +3110,14 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) 
		return ret;



	mutex_lock(&cgroup_tree_mutex);

	mutex_lock(&cgroup_mutex);



	list_add_tail(&cfts->node, &ss->cfts);

	ret = cgroup_apply_cftypes(cfts, true);

	if (ret)

		cgroup_rm_cftypes_locked(cfts);



	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&cgroup_tree_mutex);

	return ret;

}
@@ -4445,6 +4451,7 @@ static void css_killed_ref_fn(struct percpu_ref *ref) 
static void kill_css(struct cgroup_subsys_state *css)

{

	lockdep_assert_held(&cgroup_tree_mutex);

	lockdep_assert_held(&cgroup_mutex);



	/*

	 * This must happen before css is disassociated with its cgroup.
@@ -4544,13 +4551,10 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	/*

	 * Initiate massacre of all css's.  cgroup_destroy_css_killed()

	 * will be invoked to perform the rest of destruction once the

	 * percpu refs of all css's are confirmed to be killed.  This

	 * involves removing the subsystem's files, drop cgroup_mutex.

	 * percpu refs of all css's are confirmed to be killed.

	 */

	mutex_unlock(&cgroup_mutex);

	for_each_css(css, ssid, cgrp)

		kill_css(css);

	mutex_lock(&cgroup_mutex);



	/* CGRP_DEAD is set, remove from ->release_list for the last time */

	raw_spin_lock(&release_list_lock);
@@ -4567,10 +4571,11 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	if (!cgrp->nr_css)

		cgroup_destroy_css_killed(cgrp);



	/* remove @cgrp directory along with the base files */

	mutex_unlock(&cgroup_mutex);

	kernfs_remove(cgrp->kn);	/* @cgrp has an extra ref on its kn */

	mutex_lock(&cgroup_mutex);

	/*

	 * Remove @cgrp directory along with the base files.  @cgrp has an

	 * extra ref on its kn.

	 */

	kernfs_remove(cgrp->kn);



	return 0;

};