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Commit a4ea1cc9 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: always use RCU accessors for protected accesses 



kernel/cgroup.c still has places where a RCU pointer is set and
accessed directly without going through RCU_INIT_POINTER() or
rcu_dereference_protected().  They're all properly protected accesses
so nothing is broken but it leads to spurious sparse RCU address space
warnings.

Substitute direct accesses with RCU_INIT_POINTER() and
rcu_dereference_protected().  Note that %true is specified as the
extra condition for all derference updates.  This isn't ideal as all
it does is suppressing warning without actually policing
synchronization rules; however, most are scheduled to be removed
pretty soon along with css_id itself, so no reason to be more
elaborate.

Combined with the previous changes, this removes all RCU related
sparse warnings from cgroup.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatarFengguang Wu <fengguang.wu@intel.com>
Acked-by; Li Zefan <lizefan@huawei.com>
parent a8ad805c

kernel/cgroup.c

+12 −9
Original line number Original line Diff line number Diff line
@@ -1427,7 +1427,7 @@ static void init_cgroup_root(struct cgroupfs_root *root) 
	INIT_LIST_HEAD(&root->root_list);

	INIT_LIST_HEAD(&root->root_list);

	root->number_of_cgroups = 1;

	root->number_of_cgroups = 1;

	cgrp->root = root;

	cgrp->root = root;

	cgrp->name = &root_cgroup_name;

	RCU_INIT_POINTER(cgrp->name, &root_cgroup_name);

	init_cgroup_housekeeping(cgrp);

	init_cgroup_housekeeping(cgrp);

}

}
@@ -2558,7 +2558,7 @@ static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry, 
		return ret;

		return ret;

	}

	}





	old_name = cgrp->name;

	old_name = rcu_dereference_protected(cgrp->name, true);

	rcu_assign_pointer(cgrp->name, name);

	rcu_assign_pointer(cgrp->name, name);





	kfree_rcu(old_name, rcu_head);

	kfree_rcu(old_name, rcu_head);
@@ -4177,13 +4177,15 @@ static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files, 
	/* This cgroup is ready now */

	/* This cgroup is ready now */

	for_each_root_subsys(cgrp->root, ss) {

	for_each_root_subsys(cgrp->root, ss) {

		struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];

		struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];

		struct css_id *id = rcu_dereference_protected(css->id, true);



		/*

		/*

		 * Update id->css pointer and make this css visible from

		 * Update id->css pointer and make this css visible from

		 * CSS ID functions. This pointer will be dereferened

		 * CSS ID functions. This pointer will be dereferened

		 * from RCU-read-side without locks.

		 * from RCU-read-side without locks.

		 */

		 */

		if (css->id)

		if (id)

			rcu_assign_pointer(css->id->css, css);

			rcu_assign_pointer(id->css, css);

	}

	}





	return 0;

	return 0;
@@ -4863,7 +4865,7 @@ int __init cgroup_init_early(void) 
	css_set_count = 1;

	css_set_count = 1;

	init_cgroup_root(&cgroup_dummy_root);

	init_cgroup_root(&cgroup_dummy_root);

	cgroup_root_count = 1;

	cgroup_root_count = 1;

	init_task.cgroups = &init_css_set;

	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);





	init_cgrp_cset_link.cset = &init_css_set;

	init_cgrp_cset_link.cset = &init_css_set;

	init_cgrp_cset_link.cgrp = cgroup_dummy_top;

	init_cgrp_cset_link.cgrp = cgroup_dummy_top;
@@ -5380,7 +5382,8 @@ bool css_is_ancestor(struct cgroup_subsys_state *child, 




void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)

void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)

{

{

	struct css_id *id = css->id;

	struct css_id *id = rcu_dereference_protected(css->id, true);



	/* When this is called before css_id initialization, id can be NULL */

	/* When this is called before css_id initialization, id can be NULL */

	if (!id)

	if (!id)

		return;

		return;
@@ -5446,8 +5449,8 @@ static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss, 
		return PTR_ERR(newid);

		return PTR_ERR(newid);





	newid->stack[0] = newid->id;

	newid->stack[0] = newid->id;

	newid->css = rootcss;

	RCU_INIT_POINTER(newid->css, rootcss);

	rootcss->id = newid;

	RCU_INIT_POINTER(rootcss->id, newid);

	return 0;

	return 0;

}

}
@@ -5461,7 +5464,7 @@ static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent, 
	subsys_id = ss->subsys_id;

	subsys_id = ss->subsys_id;

	parent_css = parent->subsys[subsys_id];

	parent_css = parent->subsys[subsys_id];

	child_css = child->subsys[subsys_id];

	child_css = child->subsys[subsys_id];

	parent_id = parent_css->id;

	parent_id = rcu_dereference_protected(parent_css->id, true);

	depth = parent_id->depth + 1;

	depth = parent_id->depth + 1;





	child_id = get_new_cssid(ss, depth);

	child_id = get_new_cssid(ss, depth);