Commit 486eff6a authored by Yafang Shao's avatar Yafang Shao Committed by Chen Ridong
Browse files

cgroup: Make operations on the cgroup root_list RCU safe 

stable inclusion
from stable-v6.6.47
commit dd9542ae7c7ca82ed2d7c185754ba9026361f6bc
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IAP55A

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dd9542ae7c7ca82ed2d7c185754ba9026361f6bc



--------------------------------

commit d23b5c577715892c87533b13923306acc6243f93 upstream.

At present, when we perform operations on the cgroup root_list, we must
hold the cgroup_mutex, which is a relatively heavyweight lock. In reality,
we can make operations on this list RCU-safe, eliminating the need to hold
the cgroup_mutex during traversal. Modifications to the list only occur in
the cgroup root setup and destroy paths, which should be infrequent in a
production environment. In contrast, traversal may occur frequently.
Therefore, making it RCU-safe would be beneficial.

Signed-off-by: default avatarYafang Shao <laoar.shao@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
To: Michal Koutný <mkoutny@suse.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarChen Ridong <chenridong@huawei.com>
parent e52b7034

include/linux/cgroup-defs.h

+1 −0
Original line number Diff line number Diff line
@@ -591,6 +591,7 @@ struct cgroup_root { 


	/* A list running through the active hierarchies */

	struct list_head root_list;

	struct rcu_head rcu;



	/* Hierarchy-specific flags */

	unsigned int flags;

kernel/cgroup/cgroup-internal.h

+2 −1
Original line number Diff line number Diff line
@@ -170,7 +170,8 @@ extern struct list_head cgroup_roots; 


/* iterate across the hierarchies */

#define for_each_root(root)						\

	list_for_each_entry((root), &cgroup_roots, root_list)

	list_for_each_entry_rcu((root), &cgroup_roots, root_list,	\

				lockdep_is_held(&cgroup_mutex))



/**

 * for_each_subsys - iterate all enabled cgroup subsystems

kernel/cgroup/cgroup.c

+16 −7
Original line number Diff line number Diff line
@@ -1315,7 +1315,7 @@ static void cgroup_exit_root_id(struct cgroup_root *root) 


void cgroup_free_root(struct cgroup_root *root)

{

	kfree(root);

	kfree_rcu(root, rcu);

}



static void cgroup_destroy_root(struct cgroup_root *root)
@@ -1348,7 +1348,7 @@ static void cgroup_destroy_root(struct cgroup_root *root) 
	spin_unlock_irq(&css_set_lock);



	if (!list_empty(&root->root_list)) {

		list_del(&root->root_list);

		list_del_rcu(&root->root_list);

		cgroup_root_count--;

	}
@@ -1388,7 +1388,15 @@ static inline struct cgroup *__cset_cgroup_from_root(struct css_set *cset, 
		}

	}



	BUG_ON(!res_cgroup);

	/*

	 * If cgroup_mutex is not held, the cgrp_cset_link will be freed

	 * before we remove the cgroup root from the root_list. Consequently,

	 * when accessing a cgroup root, the cset_link may have already been

	 * freed, resulting in a NULL res_cgroup. However, by holding the

	 * cgroup_mutex, we ensure that res_cgroup can't be NULL.

	 * If we don't hold cgroup_mutex in the caller, we must do the NULL

	 * check.

	 */

	return res_cgroup;

}
@@ -1447,7 +1455,6 @@ static struct cgroup *current_cgns_cgroup_dfl(void) 
static struct cgroup *cset_cgroup_from_root(struct css_set *cset,

					    struct cgroup_root *root)

{

	lockdep_assert_held(&cgroup_mutex);

	lockdep_assert_held(&css_set_lock);



	return __cset_cgroup_from_root(cset, root);
@@ -1455,7 +1462,9 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset, 


/*

 * Return the cgroup for "task" from the given hierarchy. Must be

 * called with cgroup_mutex and css_set_lock held.

 * called with css_set_lock held to prevent task's groups from being modified.

 * Must be called with either cgroup_mutex or rcu read lock to prevent the

 * cgroup root from being destroyed.

 */

struct cgroup *task_cgroup_from_root(struct task_struct *task,

				     struct cgroup_root *root)
@@ -2030,7 +2039,7 @@ void init_cgroup_root(struct cgroup_fs_context *ctx) 
	struct cgroup_root *root = ctx->root;

	struct cgroup *cgrp = &root->cgrp;



	INIT_LIST_HEAD(&root->root_list);

	INIT_LIST_HEAD_RCU(&root->root_list);

	atomic_set(&root->nr_cgrps, 1);

	cgrp->root = root;

	init_cgroup_housekeeping(cgrp);
@@ -2114,7 +2123,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask) 
	 * care of subsystems' refcounts, which are explicitly dropped in

	 * the failure exit path.

	 */

	list_add(&root->root_list, &cgroup_roots);

	list_add_rcu(&root->root_list, &cgroup_roots);

	cgroup_root_count++;



	/*