This is a note to let you know that I've just added the patch titled
cgroup: Make operations on the cgroup root_list RCU safe
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cgroup-make-operations-on-the-cgroup-root_list-rcu-s.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 5d77b33fb5d57c6bd0848c810974dff0b0649b63
Author: Yafang Shao <laoar.shao@xxxxxxxxx>
Date: Sun Oct 29 06:14:29 2023 +0000
cgroup: Make operations on the cgroup root_list RCU safe
[ 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@xxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 6c6323a01d430..e0e03c68000f0 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -512,6 +512,7 @@ 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;
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index d8fcc139ac05d..f38f56b8cc416 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -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
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 643d8e178f7b9..66970b74106c8 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1304,7 +1304,7 @@ 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)
@@ -1337,7 +1337,7 @@ 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--;
}
@@ -1382,7 +1382,6 @@ current_cgns_cgroup_from_root(struct cgroup_root *root)
}
rcu_read_unlock();
- BUG_ON(!res);
return res;
}
@@ -1392,7 +1391,6 @@ 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) {
@@ -1418,7 +1416,9 @@ 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)
@@ -1950,7 +1950,7 @@ 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);
@@ -2028,7 +2028,7 @@ 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++;
/*
