Commit 46307fd6 authored by Michal Koutný's avatar Michal Koutný Committed by Tejun Heo
Browse files

cgroup: Reorganize css_set_lock and kernfs path processing 



The commit 74e4b956 incorrectly wrapped kernfs_walk_and_get
(might_sleep) under css_set_lock (spinlock). css_set_lock is needed by
__cset_cgroup_from_root to ensure stable cset->cgrp_links but not for
kernfs_walk_and_get.

We only need to make sure that the returned root_cgrp won't be freed
under us. This is given in the case of global root because it is static
(cgrp_dfl_root.cgrp). When the root_cgrp is lower in the hierarchy, it
is pinned by cgroup_ns->root_cset (and `current` task cannot switch
namespace asynchronously so ns_proxy pins cgroup_ns).

Note this reasoning won't hold for root cgroups in v1 hierarchies,
therefore create a special-cased helper function just for the default
hierarchy.

Fixes: 74e4b956 ("cgroup: Honor caller's cgroup NS when resolving path")
Reported-by: default avatarDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: default avatarMichal Koutný <mkoutny@suse.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 4de65c58

kernel/cgroup/cgroup.c

+27 −13
Original line number Diff line number Diff line
@@ -1392,6 +1392,9 @@ static void cgroup_destroy_root(struct cgroup_root *root) 
	cgroup_free_root(root);

}



/*

 * Returned cgroup is without refcount but it's valid as long as cset pins it.

 */

static inline struct cgroup *__cset_cgroup_from_root(struct css_set *cset,

					    struct cgroup_root *root)

{
@@ -1403,6 +1406,7 @@ static inline struct cgroup *__cset_cgroup_from_root(struct css_set *cset, 
		res_cgroup = cset->dfl_cgrp;

	} else {

		struct cgrp_cset_link *link;

		lockdep_assert_held(&css_set_lock);



		list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {

			struct cgroup *c = link->cgrp;
@@ -1414,6 +1418,7 @@ static inline struct cgroup *__cset_cgroup_from_root(struct css_set *cset, 
		}

	}



	BUG_ON(!res_cgroup);

	return res_cgroup;

}
@@ -1436,23 +1441,36 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) 


	rcu_read_unlock();



	BUG_ON(!res);

	return res;

}



/*

 * Look up cgroup associated with current task's cgroup namespace on the default

 * hierarchy.

 *

 * Unlike current_cgns_cgroup_from_root(), this doesn't need locks:

 * - Internal rcu_read_lock is unnecessary because we don't dereference any rcu

 *   pointers.

 * - css_set_lock is not needed because we just read cset->dfl_cgrp.

 * - As a bonus returned cgrp is pinned with the current because it cannot

 *   switch cgroup_ns asynchronously.

 */

static struct cgroup *current_cgns_cgroup_dfl(void)

{

	struct css_set *cset;



	cset = current->nsproxy->cgroup_ns->root_cset;

	return __cset_cgroup_from_root(cset, &cgrp_dfl_root);

}



/* look up cgroup associated with given css_set on the specified hierarchy */

static struct cgroup *cset_cgroup_from_root(struct css_set *cset,

					    struct cgroup_root *root)

{

	struct cgroup *res = NULL;



	lockdep_assert_held(&cgroup_mutex);

	lockdep_assert_held(&css_set_lock);



	res = __cset_cgroup_from_root(cset, root);



	BUG_ON(!res);

	return res;

	return __cset_cgroup_from_root(cset, root);

}



/*
@@ -6105,9 +6123,7 @@ struct cgroup *cgroup_get_from_id(u64 id) 
	if (!cgrp)

		return ERR_PTR(-ENOENT);



	spin_lock_irq(&css_set_lock);

	root_cgrp = current_cgns_cgroup_from_root(&cgrp_dfl_root);

	spin_unlock_irq(&css_set_lock);

	root_cgrp = current_cgns_cgroup_dfl();

	if (!cgroup_is_descendant(cgrp, root_cgrp)) {

		cgroup_put(cgrp);

		return ERR_PTR(-ENOENT);
@@ -6686,10 +6702,8 @@ struct cgroup *cgroup_get_from_path(const char *path) 
	struct cgroup *cgrp = ERR_PTR(-ENOENT);

	struct cgroup *root_cgrp;



	spin_lock_irq(&css_set_lock);

	root_cgrp = current_cgns_cgroup_from_root(&cgrp_dfl_root);

	root_cgrp = current_cgns_cgroup_dfl();

	kn = kernfs_walk_and_get(root_cgrp->kn, path);

	spin_unlock_irq(&css_set_lock);

	if (!kn)

		goto out;