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cgroup: css iterations and css_from_dir() are safe under cgroup_mutex 

Currently, all css iterations and css_from_dir() require RCU read lock
whether the caller is holding cgroup_mutex or not, which is
unnecessarily restrictive.  They are all safe to use under
cgroup_mutex without holding RCU read lock.

Factor out cgroup_assert_mutex_or_rcu_locked() from css_from_id() and
apply it to all css iteration functions and css_from_dir().

v2: cgroup_assert_mutex_or_rcu_locked() definition doesn't need to be
    inside CONFIG_PROVE_RCU ifdef as rcu_lockdep_assert() is always
    defined and conditionalized.  Move it outside of the ifdef block.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-12-06 15:11:55 -05:00
parent e58e1ca438
commit 87fb54f1b5
1 changed files with 30 additions and 26 deletions
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56
kernel/cgroup.c
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@ -93,6 +93,11 @@ static DEFINE_MUTEX(cgroup_mutex);
static DEFINE_MUTEX(cgroup_root_mutex);
#define cgroup_assert_mutex_or_rcu_locked() \
rcu_lockdep_assert(rcu_read_lock_held() || \
lockdep_is_held(&cgroup_mutex), \
"cgroup_mutex or RCU read lock required");
/*
* cgroup destruction makes heavy use of work items and there can be a lot
* of concurrent destructions. Use a separate workqueue so that cgroup
@ -2897,9 +2902,9 @@ static void cgroup_enable_task_cg_lists(void)
* @parent_css: css whose children to walk
*
* This function returns the next child of @parent_css and should be called
* under RCU read lock. The only requirement is that @parent_css and
* @pos_css are accessible. The next sibling is guaranteed to be returned
* regardless of their states.
* under either cgroup_mutex or RCU read lock. The only requirement is
* that @parent_css and @pos_css are accessible. The next sibling is
* guaranteed to be returned regardless of their states.
*/
struct cgroup_subsys_state *
css_next_child(struct cgroup_subsys_state *pos_css,
@ -2909,7 +2914,7 @@ css_next_child(struct cgroup_subsys_state *pos_css,
struct cgroup *cgrp = parent_css->cgroup;
struct cgroup *next;
WARN_ON_ONCE(!rcu_read_lock_held());
cgroup_assert_mutex_or_rcu_locked();
/*
* @pos could already have been removed. Once a cgroup is removed,
@ -2956,10 +2961,10 @@ EXPORT_SYMBOL_GPL(css_next_child);
* to visit for pre-order traversal of @root's descendants. @root is
* included in the iteration and the first node to be visited.
*
* While this function requires RCU read locking, it doesn't require the
* whole traversal to be contained in a single RCU critical section. This
* function will return the correct next descendant as long as both @pos
* and @root are accessible and @pos is a descendant of @root.
* While this function requires cgroup_mutex or RCU read locking, it
* doesn't require the whole traversal to be contained in a single critical
* section. This function will return the correct next descendant as long
* as both @pos and @root are accessible and @pos is a descendant of @root.
*/
struct cgroup_subsys_state *
css_next_descendant_pre(struct cgroup_subsys_state *pos,
@ -2967,7 +2972,7 @@ css_next_descendant_pre(struct cgroup_subsys_state *pos,
{
struct cgroup_subsys_state *next;
WARN_ON_ONCE(!rcu_read_lock_held());
cgroup_assert_mutex_or_rcu_locked();
/* if first iteration, visit @root */
if (!pos)
@ -2998,17 +3003,17 @@ EXPORT_SYMBOL_GPL(css_next_descendant_pre);
* is returned. This can be used during pre-order traversal to skip
* subtree of @pos.
*
* While this function requires RCU read locking, it doesn't require the
* whole traversal to be contained in a single RCU critical section. This
* function will return the correct rightmost descendant as long as @pos is
* accessible.
* While this function requires cgroup_mutex or RCU read locking, it
* doesn't require the whole traversal to be contained in a single critical
* section. This function will return the correct rightmost descendant as
* long as @pos is accessible.
*/
struct cgroup_subsys_state *
css_rightmost_descendant(struct cgroup_subsys_state *pos)
{
struct cgroup_subsys_state *last, *tmp;
WARN_ON_ONCE(!rcu_read_lock_held());
cgroup_assert_mutex_or_rcu_locked();
do {
last = pos;
@ -3044,10 +3049,11 @@ css_leftmost_descendant(struct cgroup_subsys_state *pos)
* to visit for post-order traversal of @root's descendants. @root is
* included in the iteration and the last node to be visited.
*
* While this function requires RCU read locking, it doesn't require the
* whole traversal to be contained in a single RCU critical section. This
* function will return the correct next descendant as long as both @pos
* and @cgroup are accessible and @pos is a descendant of @cgroup.
* While this function requires cgroup_mutex or RCU read locking, it
* doesn't require the whole traversal to be contained in a single critical
* section. This function will return the correct next descendant as long
* as both @pos and @cgroup are accessible and @pos is a descendant of
* @cgroup.
*/
struct cgroup_subsys_state *
css_next_descendant_post(struct cgroup_subsys_state *pos,
@ -3055,7 +3061,7 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
{
struct cgroup_subsys_state *next;
WARN_ON_ONCE(!rcu_read_lock_held());
cgroup_assert_mutex_or_rcu_locked();
/* if first iteration, visit leftmost descendant which may be @root */
if (!pos)
@ -5217,16 +5223,16 @@ __setup("cgroup_disable=", cgroup_disable);
* @dentry: directory dentry of interest
* @ss: subsystem of interest
*
* Must be called under RCU read lock. The caller is responsible for
* pinning the returned css if it needs to be accessed outside the RCU
* critical section.
* Must be called under cgroup_mutex or RCU read lock. The caller is
* responsible for pinning the returned css if it needs to be accessed
* outside the critical section.
*/
struct cgroup_subsys_state *css_from_dir(struct dentry *dentry,
struct cgroup_subsys *ss)
{
struct cgroup *cgrp;
WARN_ON_ONCE(!rcu_read_lock_held());
cgroup_assert_mutex_or_rcu_locked();
/* is @dentry a cgroup dir? */
if (!dentry->d_inode ||
@ -5249,9 +5255,7 @@ struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)
{
struct cgroup *cgrp;
rcu_lockdep_assert(rcu_read_lock_held() ||
lockdep_is_held(&cgroup_mutex),
"css_from_id() needs proper protection");
cgroup_assert_mutex_or_rcu_locked();
cgrp = idr_find(&ss->root->cgroup_idr, id);
if (cgrp)