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cgroup: Make operations on the cgroup root_list RCU safe

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[ Upstream commit d23b5c5777 ]

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: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Yafang Shao 2023-10-29 06:14:29 +00:00 committed by Greg Kroah-Hartman
parent c031d286ec
commit de77545c72
3 changed files with 10 additions and 8 deletions
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1
include/linux/cgroup-defs.h
View File

@ -516,6 +516,7 @@ 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;

3
kernel/cgroup/cgroup-internal.h
View File

@ -172,7 +172,8 @@ 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

14
kernel/cgroup/cgroup.c
View File

@ -1332,7 +1332,7 @@ 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)
@ -1365,7 +1365,7 @@ 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--;
}
@ -1411,7 +1411,6 @@ current_cgns_cgroup_from_root(struct cgroup_root *root)
}
rcu_read_unlock();
BUG_ON(!res);
return res;
}
@ -1421,7 +1420,6 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
{
struct cgroup *res = NULL;
lockdep_assert_held(&cgroup_mutex);
lockdep_assert_held(&css_set_lock);
if (cset == &init_css_set) {
@ -1447,7 +1445,9 @@ 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)
@ -1986,7 +1986,7 @@ 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);
@ -2068,7 +2068,7 @@ 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++;
/*