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Message-ID: <20250920005931.2753828-20-tj@kernel.org>
Date: Fri, 19 Sep 2025 14:58:42 -1000
From: Tejun Heo <tj@...nel.org>
To: void@...ifault.com,
arighi@...dia.com,
multics69@...il.com
Cc: linux-kernel@...r.kernel.org,
sched-ext@...ts.linux.dev,
memxor@...il.com,
bpf@...r.kernel.org,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 19/46] cgroup: Expose some cgroup helpers
Expose the following through cgroup.h:
- cgroup_on_dfl()
- cgroup_is_dead()
- cgroup_for_each_live_child()
- cgroup_for_each_live_descendant_pre()
- cgroup_for_each_live_descendant_post()
Until now, these didn't need to be exposed because controllers only cared
about the css hierarchy. The planned sched_ext hierarchical scheduler
support will be based on the default cgroup hierarchy, which is in line
with the existing BPF cgroup support, and thus needs these exposed.
Signed-off-by: Tejun Heo <tj@...nel.org>
---
include/linux/cgroup.h | 65 ++++++++++++++++++++++++++++++++-
kernel/cgroup/cgroup-internal.h | 6 ---
kernel/cgroup/cgroup.c | 55 ----------------------------
3 files changed, 63 insertions(+), 63 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b18fb5fcb38e..3abdff370dd3 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -41,6 +41,14 @@ struct kernel_clone_args;
#ifdef CONFIG_CGROUPS
+/*
+ * To avoid confusing the compiler (and generating warnings) with code
+ * that attempts to access what would be a 0-element array (i.e. sized
+ * to a potentially empty array when CGROUP_SUBSYS_COUNT == 0), this
+ * constant expression can be added.
+ */
+#define CGROUP_HAS_SUBSYS_CONFIG (CGROUP_SUBSYS_COUNT > 0)
+
enum css_task_iter_flags {
CSS_TASK_ITER_PROCS = (1U << 0), /* walk only threadgroup leaders */
CSS_TASK_ITER_THREADED = (1U << 1), /* walk all threaded css_sets in the domain */
@@ -75,6 +83,7 @@ enum cgroup_lifetime_events {
extern struct file_system_type cgroup_fs_type;
extern struct cgroup_root cgrp_dfl_root;
extern struct css_set init_css_set;
+extern struct mutex cgroup_mutex;
extern spinlock_t css_set_lock;
extern struct blocking_notifier_head cgroup_lifetime_notifier;
@@ -102,6 +111,8 @@ extern struct blocking_notifier_head cgroup_lifetime_notifier;
#define cgroup_subsys_on_dfl(ss) \
static_branch_likely(&ss ## _on_dfl_key)
+bool cgroup_on_dfl(const struct cgroup *cgrp);
+
bool css_has_online_children(struct cgroup_subsys_state *css);
struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss);
struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgroup,
@@ -272,6 +283,32 @@ void css_task_iter_end(struct css_task_iter *it);
for ((pos) = css_next_descendant_post(NULL, (css)); (pos); \
(pos) = css_next_descendant_post((pos), (css)))
+/* iterate over child cgrps, lock should be held throughout iteration */
+#define cgroup_for_each_live_child(child, cgrp) \
+ list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
+ if (({ lockdep_assert_held(&cgroup_mutex); \
+ cgroup_is_dead(child); })) \
+ ; \
+ else
+
+/* walk live descendants in pre order */
+#define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) \
+ css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL)) \
+ if (({ lockdep_assert_held(&cgroup_mutex); \
+ (dsct) = (d_css)->cgroup; \
+ cgroup_is_dead(dsct); })) \
+ ; \
+ else
+
+/* walk live descendants in postorder */
+#define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) \
+ css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
+ if (({ lockdep_assert_held(&cgroup_mutex); \
+ (dsct) = (d_css)->cgroup; \
+ cgroup_is_dead(dsct); })) \
+ ; \
+ else
+
/**
* cgroup_taskset_for_each - iterate cgroup_taskset
* @task: the loop cursor
@@ -334,6 +371,27 @@ static inline u64 cgroup_id(const struct cgroup *cgrp)
return cgrp->kn->id;
}
+/**
+ * cgroup_css - obtain a cgroup's css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest (%NULL returns @cgrp->self)
+ *
+ * Return @cgrp's css (cgroup_subsys_state) associated with @ss. This
+ * function must be called either under cgroup_mutex or rcu_read_lock() and
+ * the caller is responsible for pinning the returned css if it wants to
+ * keep accessing it outside the said locks. This function may return
+ * %NULL if @cgrp doesn't have @subsys_id enabled.
+ */
+static inline struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
+ struct cgroup_subsys *ss)
+{
+ if (CGROUP_HAS_SUBSYS_CONFIG && ss)
+ return rcu_dereference_check(cgrp->subsys[ss->id],
+ lockdep_is_held(&cgroup_mutex));
+ else
+ return &cgrp->self;
+}
+
/**
* css_is_dying - test whether the specified css is dying
* @css: target css
@@ -365,6 +423,11 @@ static inline bool css_is_self(struct cgroup_subsys_state *css)
return false;
}
+static inline bool cgroup_is_dead(const struct cgroup *cgrp)
+{
+ return !(cgrp->self.flags & CSS_ONLINE);
+}
+
static inline void cgroup_get(struct cgroup *cgrp)
{
css_get(&cgrp->self);
@@ -380,8 +443,6 @@ static inline void cgroup_put(struct cgroup *cgrp)
css_put(&cgrp->self);
}
-extern struct mutex cgroup_mutex;
-
static inline void cgroup_lock(void)
{
mutex_lock(&cgroup_mutex);
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index b14e61c64a34..31b6f4cb05ba 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -184,11 +184,6 @@ extern bool cgrp_dfl_visible;
for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \
(((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
-static inline bool cgroup_is_dead(const struct cgroup *cgrp)
-{
- return !(cgrp->self.flags & CSS_ONLINE);
-}
-
static inline bool notify_on_release(const struct cgroup *cgrp)
{
return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
@@ -222,7 +217,6 @@ static inline void get_css_set(struct css_set *cset)
}
bool cgroup_ssid_enabled(int ssid);
-bool cgroup_on_dfl(const struct cgroup *cgrp);
struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root);
struct cgroup *task_cgroup_from_root(struct task_struct *task,
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 312c6a8b55bb..4107af27965f 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -69,14 +69,6 @@
/* let's not notify more than 100 times per second */
#define CGROUP_FILE_NOTIFY_MIN_INTV DIV_ROUND_UP(HZ, 100)
-/*
- * To avoid confusing the compiler (and generating warnings) with code
- * that attempts to access what would be a 0-element array (i.e. sized
- * to a potentially empty array when CGROUP_SUBSYS_COUNT == 0), this
- * constant expression can be added.
- */
-#define CGROUP_HAS_SUBSYS_CONFIG (CGROUP_SUBSYS_COUNT > 0)
-
/*
* cgroup_mutex is the master lock. Any modification to cgroup or its
* hierarchy must be performed while holding it.
@@ -480,27 +472,6 @@ static u16 cgroup_ss_mask(struct cgroup *cgrp)
return cgrp->root->subsys_mask;
}
-/**
- * cgroup_css - obtain a cgroup's css for the specified subsystem
- * @cgrp: the cgroup of interest
- * @ss: the subsystem of interest (%NULL returns @cgrp->self)
- *
- * Return @cgrp's css (cgroup_subsys_state) associated with @ss. This
- * function must be called either under cgroup_mutex or rcu_read_lock() and
- * the caller is responsible for pinning the returned css if it wants to
- * keep accessing it outside the said locks. This function may return
- * %NULL if @cgrp doesn't have @subsys_id enabled.
- */
-static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
- struct cgroup_subsys *ss)
-{
- if (CGROUP_HAS_SUBSYS_CONFIG && ss)
- return rcu_dereference_check(cgrp->subsys[ss->id],
- lockdep_is_held(&cgroup_mutex));
- else
- return &cgrp->self;
-}
-
/**
* cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
* @cgrp: the cgroup of interest
@@ -712,32 +683,6 @@ EXPORT_SYMBOL_GPL(of_css);
} \
} while (false)
-/* iterate over child cgrps, lock should be held throughout iteration */
-#define cgroup_for_each_live_child(child, cgrp) \
- list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
- if (({ lockdep_assert_held(&cgroup_mutex); \
- cgroup_is_dead(child); })) \
- ; \
- else
-
-/* walk live descendants in pre order */
-#define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) \
- css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL)) \
- if (({ lockdep_assert_held(&cgroup_mutex); \
- (dsct) = (d_css)->cgroup; \
- cgroup_is_dead(dsct); })) \
- ; \
- else
-
-/* walk live descendants in postorder */
-#define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) \
- css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
- if (({ lockdep_assert_held(&cgroup_mutex); \
- (dsct) = (d_css)->cgroup; \
- cgroup_is_dead(dsct); })) \
- ; \
- else
-
/*
* The default css_set - used by init and its children prior to any
* hierarchies being mounted. It contains a pointer to the root state
--
2.51.0
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