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cgroup: Make operations on the cgroup root_list RCU safe

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[ Upstream commit d23b5c577715892c87533b13923306acc6243f93 ]

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 Ksawlii
parent e5a4f3990a
commit 6c357bd6a8
3 changed files with 10 additions and 8 deletions
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1
include/linux/cgroup-defs.h
View file

@ -519,6 +519,7 @@ struct cgroup_root {
/* A list running through the active hierarchies */ /* A list running through the active hierarchies */
struct list_head root_list; struct list_head root_list;
struct rcu_head rcu;
/* Hierarchy-specific flags */ /* Hierarchy-specific flags */
unsigned int 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 */ /* iterate across the hierarchies */
#define for_each_root(root) \ #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 * for_each_subsys - iterate all enabled cgroup subsystems

14
kernel/cgroup/cgroup.c
View file

@ -1328,7 +1328,7 @@ static void cgroup_exit_root_id(struct cgroup_root *root)
void cgroup_free_root(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) static void cgroup_destroy_root(struct cgroup_root *root)
@ -1361,7 +1361,7 @@ static void cgroup_destroy_root(struct cgroup_root *root)
spin_unlock_irq(&css_set_lock); spin_unlock_irq(&css_set_lock);
if (!list_empty(&root->root_list)) { if (!list_empty(&root->root_list)) {
list_del(&root->root_list); list_del_rcu(&root->root_list);
cgroup_root_count--; cgroup_root_count--;
} }
@ -1406,7 +1406,6 @@ current_cgns_cgroup_from_root(struct cgroup_root *root)
} }
rcu_read_unlock(); rcu_read_unlock();
BUG_ON(!res);
return res; return res;
} }
@ -1416,7 +1415,6 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
{ {
struct cgroup *res = NULL; struct cgroup *res = NULL;
lockdep_assert_held(&cgroup_mutex);
lockdep_assert_held(&css_set_lock); lockdep_assert_held(&css_set_lock);
if (cset == &init_css_set) { if (cset == &init_css_set) {
@ -1442,7 +1440,9 @@ static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
/* /*
* Return the cgroup for "task" from the given hierarchy. Must be * 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 *task_cgroup_from_root(struct task_struct *task,
struct cgroup_root *root) struct cgroup_root *root)
@ -1974,7 +1974,7 @@ void init_cgroup_root(struct cgroup_fs_context *ctx)
struct cgroup_root *root = ctx->root; struct cgroup_root *root = ctx->root;
struct cgroup *cgrp = &root->cgrp; struct cgroup *cgrp = &root->cgrp;
INIT_LIST_HEAD(&root->root_list); INIT_LIST_HEAD_RCU(&root->root_list);
atomic_set(&root->nr_cgrps, 1); atomic_set(&root->nr_cgrps, 1);
cgrp->root = root; cgrp->root = root;
init_cgroup_housekeeping(cgrp); init_cgroup_housekeeping(cgrp);
@ -2052,7 +2052,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
* care of subsystems' refcounts, which are explicitly dropped in * care of subsystems' refcounts, which are explicitly dropped in
* the failure exit path. * the failure exit path.
*/ */
list_add(&root->root_list, &cgroup_roots); list_add_rcu(&root->root_list, &cgroup_roots);
cgroup_root_count++; cgroup_root_count++;
/* /*