Message-Id: <20210413044133.617921-2-namhyung@kernel.org>
Date:   Mon, 12 Apr 2021 21:41:32 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Song Liu <songliubraving@...com>, Tejun Heo <tj@...nel.org>
Subject: [PATCH v2 1/2] perf/core: Share an event with multiple cgroups

As we can run many jobs (in container) on a big machine, we want to
measure each job's performance during the run.  To do that, the
perf_event can be associated to a cgroup to measure it only.

However such cgroup events need to be opened separately and it causes
significant overhead in event multiplexing during the context switch
as well as resource consumption like in file descriptors and memory
footprint.

As a cgroup event is basically a cpu event, we can share a single cpu
event for multiple cgroups.  All we need is a separate counter (and
two timing variables) for each cgroup.  I added a hash table to map
from cgroup id to the attached cgroups.

With this change, the cpu event needs to calculate a delta of event
counter values when the cgroups of current and the next task are
different.  And it attributes the delta to the current task's cgroup.

This patch adds two new ioctl commands to perf_event for light-weight
cgroup event counting (i.e. perf stat).

 * PERF_EVENT_IOC_ATTACH_CGROUP - it takes a buffer consists of a
     64-bit array to attach given cgroups.  The first element is a
     number of cgroups in the buffer, and the rest is a list of cgroup
     ids to add a cgroup info to the given event.

 * PERF_EVENT_IOC_READ_CGROUP - it takes a buffer consists of a 64-bit
     array to get the event counter values.  The first element is size
     of the array in byte, and the second element is a cgroup id to
     read.  The rest is to save the counter value and timings.

This attaches all cgroups in a single syscall and I didn't add the
DETACH command deliberately to make the implementation simple.  The
attached cgroup nodes would be deleted when the file descriptor of the
perf_event is closed.

Cc: Tejun Heo <tj@...nel.org>
Acked-by: Song Liu <songliubraving@...com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 include/linux/perf_event.h      |  22 ++
 include/uapi/linux/perf_event.h |   2 +
 kernel/events/core.c            | 477 ++++++++++++++++++++++++++++++--
 3 files changed, 474 insertions(+), 27 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3f7f89ea5e51..4b03cbadf4a0 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -771,6 +771,19 @@ struct perf_event {
 
 #ifdef CONFIG_CGROUP_PERF
 	struct perf_cgroup		*cgrp; /* cgroup event is attach to */
+
+	/* to share an event for multiple cgroups */
+	struct hlist_head		*cgrp_node_hash;
+	struct perf_cgroup_node		*cgrp_node_entries;
+	int				nr_cgrp_nodes;
+	int				cgrp_node_hash_bits;
+
+	struct list_head		cgrp_node_entry;
+
+	/* snapshot of previous reading (for perf_cgroup_node below) */
+	u64				cgrp_node_count;
+	u64				cgrp_node_time_enabled;
+	u64				cgrp_node_time_running;
 #endif
 
 #ifdef CONFIG_SECURITY
@@ -780,6 +793,13 @@ struct perf_event {
 #endif /* CONFIG_PERF_EVENTS */
 };
 
+struct perf_cgroup_node {
+	struct hlist_node		node;
+	u64				id;
+	u64				count;
+	u64				time_enabled;
+	u64				time_running;
+} ____cacheline_aligned;
 
 struct perf_event_groups {
 	struct rb_root	tree;
@@ -843,6 +863,8 @@ struct perf_event_context {
 	int				pin_count;
 #ifdef CONFIG_CGROUP_PERF
 	int				nr_cgroups;	 /* cgroup evts */
+	struct list_head		cgrp_node_list;
+	struct list_head		cgrp_ctx_entry;
 #endif
 	void				*task_ctx_data; /* pmu specific data */
 	struct rcu_head			rcu_head;
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index ad15e40d7f5d..06bc7ab13616 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -479,6 +479,8 @@ struct perf_event_query_bpf {
 #define PERF_EVENT_IOC_PAUSE_OUTPUT		_IOW('$', 9, __u32)
 #define PERF_EVENT_IOC_QUERY_BPF		_IOWR('$', 10, struct perf_event_query_bpf *)
 #define PERF_EVENT_IOC_MODIFY_ATTRIBUTES	_IOW('$', 11, struct perf_event_attr *)
+#define PERF_EVENT_IOC_ATTACH_CGROUP		_IOW('$', 12, __u64 *)
+#define PERF_EVENT_IOC_READ_CGROUP		_IOWR('$', 13, __u64 *)
 
 enum perf_event_ioc_flags {
 	PERF_IOC_FLAG_GROUP		= 1U << 0,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f07943183041..0c6b3848a61f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -379,6 +379,7 @@ enum event_type_t {
  * perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu
  */
 
+static void perf_sched_enable(void);
 static void perf_sched_delayed(struct work_struct *work);
 DEFINE_STATIC_KEY_FALSE(perf_sched_events);
 static DECLARE_DELAYED_WORK(perf_sched_work, perf_sched_delayed);
@@ -2124,6 +2125,322 @@ static int perf_get_aux_event(struct perf_event *event,
 	return 1;
 }
 
+#ifdef CONFIG_CGROUP_PERF
+static DEFINE_PER_CPU(struct list_head, cgroup_ctx_list);
+
+static bool event_can_attach_cgroup(struct perf_event *event)
+{
+	if (is_sampling_event(event))
+		return false;
+	if (event->attach_state & PERF_ATTACH_TASK)
+		return false;
+	if (is_cgroup_event(event))
+		return false;
+
+	return true;
+}
+
+static bool event_has_cgroup_node(struct perf_event *event)
+{
+	return event->nr_cgrp_nodes > 0;
+}
+
+static struct perf_cgroup_node *
+find_cgroup_node(struct perf_event *event, u64 cgrp_id)
+{
+	struct perf_cgroup_node *cgrp_node;
+	int key = hash_64(cgrp_id, event->cgrp_node_hash_bits);
+
+	hlist_for_each_entry(cgrp_node, &event->cgrp_node_hash[key], node) {
+		if (cgrp_node->id == cgrp_id)
+			return cgrp_node;
+	}
+
+	return NULL;
+}
+
+static void perf_update_cgroup_node(struct perf_event *event, struct cgroup *cgrp)
+{
+	u64 delta_count, delta_time_enabled, delta_time_running;
+	int i;
+
+	if (event->cgrp_node_count == 0)
+		goto out;
+
+	delta_count = local64_read(&event->count) - event->cgrp_node_count;
+	delta_time_enabled = event->total_time_enabled - event->cgrp_node_time_enabled;
+	delta_time_running = event->total_time_running - event->cgrp_node_time_running;
+
+	/* account delta to all ancestor cgroups */
+	for (i = 0; i <= cgrp->level; i++) {
+		struct perf_cgroup_node *node;
+
+		node = find_cgroup_node(event, cgrp->ancestor_ids[i]);
+		if (node) {
+			node->count += delta_count;
+			node->time_enabled += delta_time_enabled;
+			node->time_running += delta_time_running;
+		}
+	}
+
+out:
+	event->cgrp_node_count = local64_read(&event->count);
+	event->cgrp_node_time_enabled = event->total_time_enabled;
+	event->cgrp_node_time_running = event->total_time_running;
+}
+
+static void update_cgroup_node(struct perf_event *event, struct cgroup *cgrp)
+{
+	if (event->state == PERF_EVENT_STATE_ACTIVE)
+		event->pmu->read(event);
+
+	perf_event_update_time(event);
+	perf_update_cgroup_node(event, cgrp);
+}
+
+/* this is called from context switch */
+static void update_cgroup_node_events(struct perf_event_context *ctx,
+				      struct cgroup *cgrp)
+{
+	struct perf_event *event;
+
+	lockdep_assert_held(&ctx->lock);
+
+	if (ctx->is_active & EVENT_TIME)
+		update_context_time(ctx);
+
+	list_for_each_entry(event, &ctx->cgrp_node_list, cgrp_node_entry)
+		update_cgroup_node(event, cgrp);
+}
+
+static void cgroup_node_sched_out(struct task_struct *task)
+{
+	struct list_head *cgrp_ctx_list = this_cpu_ptr(&cgroup_ctx_list);
+	struct perf_cgroup *cgrp = perf_cgroup_from_task(task, NULL);
+	struct perf_event_context *ctx;
+
+	list_for_each_entry(ctx, cgrp_ctx_list, cgrp_ctx_entry) {
+		raw_spin_lock(&ctx->lock);
+		update_cgroup_node_events(ctx, cgrp->css.cgroup);
+		raw_spin_unlock(&ctx->lock);
+	}
+}
+
+/* these are called from the when an event is enabled/disabled */
+static void perf_add_cgrp_node_list(struct perf_event *event,
+				    struct perf_event_context *ctx)
+{
+	struct list_head *cgrp_ctx_list = this_cpu_ptr(&cgroup_ctx_list);
+	struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx);
+	bool is_first;
+
+	lockdep_assert_irqs_disabled();
+	lockdep_assert_held(&ctx->lock);
+
+	is_first = list_empty(&ctx->cgrp_node_list);
+	list_add_tail(&event->cgrp_node_entry, &ctx->cgrp_node_list);
+
+	if (is_first)
+		list_add_tail(&ctx->cgrp_ctx_entry, cgrp_ctx_list);
+
+	update_cgroup_node(event, cgrp->css.cgroup);
+}
+
+static void perf_del_cgrp_node_list(struct perf_event *event,
+				    struct perf_event_context *ctx)
+{
+	struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx);
+
+	lockdep_assert_irqs_disabled();
+	lockdep_assert_held(&ctx->lock);
+
+	update_cgroup_node(event, cgrp->css.cgroup);
+	/* to refresh delta when it's enabled */
+	event->cgrp_node_count = 0;
+
+	list_del(&event->cgrp_node_entry);
+
+	if (list_empty(&ctx->cgrp_node_list))
+		list_del(&ctx->cgrp_ctx_entry);
+}
+
+static void perf_attach_cgroup_node(struct perf_event *event,
+				    struct perf_cpu_context *cpuctx,
+				    struct perf_event_context *ctx,
+				    void *data)
+{
+	if (ctx->is_active & EVENT_TIME)
+		update_context_time(ctx);
+
+	perf_add_cgrp_node_list(event, ctx);
+}
+
+#define MIN_CGRP_NODE_HASH  4
+#define MAX_CGRP_NODE_HASH  (4 * 1024)
+
+/* this is called from ioctl */
+static int perf_event_attach_cgroup_node(struct perf_event *event, u64 nr_cgrps,
+					 u64 *cgroup_ids)
+{
+	struct perf_cgroup_node *cgrp_node;
+	struct perf_event_context *ctx = event->ctx;
+	struct hlist_head *cgrp_node_hash;
+	int node = (event->cpu >= 0) ? cpu_to_node(event->cpu) : -1;
+	unsigned long flags;
+	bool is_first = true;
+	bool enabled;
+	int i, nr_hash;
+	int hash_bits;
+
+	if (nr_cgrps < MIN_CGRP_NODE_HASH)
+		nr_hash = MIN_CGRP_NODE_HASH;
+	else
+		nr_hash = roundup_pow_of_two(nr_cgrps);
+	hash_bits = ilog2(nr_hash);
+
+	cgrp_node_hash = kcalloc_node(nr_hash, sizeof(*cgrp_node_hash),
+				      GFP_KERNEL, node);
+	if (cgrp_node_hash == NULL)
+		return -ENOMEM;
+
+	cgrp_node = kcalloc_node(nr_cgrps, sizeof(*cgrp_node), GFP_KERNEL, node);
+	if (cgrp_node == NULL) {
+		kfree(cgrp_node_hash);
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < (int)nr_cgrps; i++) {
+		int key = hash_64(cgroup_ids[i], hash_bits);
+
+		cgrp_node[i].id = cgroup_ids[i];
+		hlist_add_head(&cgrp_node[i].node, &cgrp_node_hash[key]);
+	}
+
+	raw_spin_lock_irqsave(&ctx->lock, flags);
+
+	enabled = event->state >= PERF_EVENT_STATE_INACTIVE;
+
+	if (event->nr_cgrp_nodes != 0) {
+		kfree(event->cgrp_node_hash);
+		kfree(event->cgrp_node_entries);
+		is_first = false;
+	}
+
+	event->cgrp_node_hash = cgrp_node_hash;
+	event->cgrp_node_entries = cgrp_node;
+	event->cgrp_node_hash_bits = hash_bits;
+	event->nr_cgrp_nodes = nr_cgrps;
+
+	raw_spin_unlock_irqrestore(&ctx->lock, flags);
+
+	if (is_first && enabled)
+		event_function_call(event, perf_attach_cgroup_node, NULL);
+
+	return 0;
+}
+
+static void perf_event_destroy_cgroup_nodes(struct perf_event *event)
+{
+	struct perf_event_context *ctx = event->ctx;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&ctx->lock, flags);
+
+	if (event_has_cgroup_node(event)) {
+		if (!atomic_add_unless(&perf_sched_count, -1, 1))
+			schedule_delayed_work(&perf_sched_work, HZ);
+	}
+
+	kfree(event->cgrp_node_hash);
+	kfree(event->cgrp_node_entries);
+	event->nr_cgrp_nodes = 0;
+
+	raw_spin_unlock_irqrestore(&ctx->lock, flags);
+}
+
+static int perf_event_read(struct perf_event *event, bool group);
+
+static void __perf_read_cgroup_node(struct perf_event *event)
+{
+	struct perf_cgroup *cgrp;
+
+	if (event_has_cgroup_node(event)) {
+		cgrp = perf_cgroup_from_task(current, NULL);
+		perf_update_cgroup_node(event, cgrp->css.cgroup);
+	}
+}
+
+static int perf_event_read_cgroup_node(struct perf_event *event, u64 read_size,
+				       u64 cgrp_id, char __user *buf)
+{
+	struct perf_cgroup_node *cgrp;
+	struct perf_event_context *ctx = event->ctx;
+	unsigned long flags;
+	u64 read_format = event->attr.read_format;
+	u64 values[4];
+	int n = 0;
+
+	/* update event count and times (possibly run on other cpu) */
+	(void)perf_event_read(event, false);
+
+	raw_spin_lock_irqsave(&ctx->lock, flags);
+
+	cgrp = find_cgroup_node(event, cgrp_id);
+	if (cgrp == NULL) {
+		raw_spin_unlock_irqrestore(&ctx->lock, flags);
+		return -ENOENT;
+	}
+
+	values[n++] = cgrp->count;
+	if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
+		values[n++] = cgrp->time_enabled;
+	if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
+		values[n++] = cgrp->time_running;
+	if (read_format & PERF_FORMAT_ID)
+		values[n++] = primary_event_id(event);
+
+	raw_spin_unlock_irqrestore(&ctx->lock, flags);
+
+	if (copy_to_user(buf, values, n * sizeof(u64)))
+		return -EFAULT;
+
+	return n * sizeof(u64);
+}
+#else  /* !CONFIG_CGROUP_PERF */
+static inline bool event_can_attach_cgroup(struct perf_event *event)
+{
+	return false;
+}
+
+static inline bool event_has_cgroup_node(struct perf_event *event)
+{
+	return false;
+}
+
+static void cgroup_node_sched_out(struct task_struct *task) {}
+
+static inline void perf_add_cgrp_node_list(struct perf_event *event,
+					   struct perf_event_context *ctx) {}
+static inline void perf_del_cgrp_node_list(struct perf_event *event,
+					   struct perf_event_context *ctx) {}
+
+#define MAX_CGRP_NODE_HASH  1
+static inline int perf_event_attach_cgroup_node(struct perf_event *event,
+						u64 nr_cgrps, u64 *cgrp_ids)
+{
+	return -ENODEV;
+}
+
+static inline void perf_event_destroy_cgroup_nodes(struct perf_event *event) {}
+static inline  void __perf_read_cgroup_node(struct perf_event *event) {}
+
+static inline int perf_event_read_cgroup_node(struct perf_event *event,
+					      u64 cgrp_id, char __user *buf)
+{
+	return -EINVAL;
+}
+#endif  /* CONFIG_CGROUP_PERF */
+
 static inline struct list_head *get_event_list(struct perf_event *event)
 {
 	struct perf_event_context *ctx = event->ctx;
@@ -2407,6 +2724,7 @@ static void __perf_event_disable(struct perf_event *event,
 
 	perf_event_set_state(event, PERF_EVENT_STATE_OFF);
 	perf_cgroup_event_disable(event, ctx);
+	perf_del_cgrp_node_list(event, ctx);
 }
 
 /*
@@ -2946,6 +3264,7 @@ static void __perf_event_enable(struct perf_event *event,
 
 	perf_event_set_state(event, PERF_EVENT_STATE_INACTIVE);
 	perf_cgroup_event_enable(event, ctx);
+	perf_add_cgrp_node_list(event, ctx);
 
 	if (!ctx->is_active)
 		return;
@@ -3568,6 +3887,11 @@ void __perf_event_task_sched_out(struct task_struct *task,
 	 */
 	if (atomic_read(this_cpu_ptr(&perf_cgroup_events)))
 		perf_cgroup_sched_out(task, next);
+
+	if (!list_empty(this_cpu_ptr(&cgroup_ctx_list)) &&
+	    perf_cgroup_from_task(task, NULL) !=
+	    perf_cgroup_from_task(next, NULL))
+		cgroup_node_sched_out(task);
 }
 
 /*
@@ -4268,6 +4592,7 @@ static void __perf_event_read(void *info)
 
 	if (!data->group) {
 		pmu->read(event);
+		__perf_read_cgroup_node(event);
 		data->ret = 0;
 		goto unlock;
 	}
@@ -4283,6 +4608,7 @@ static void __perf_event_read(void *info)
 			 * sibling could be on different (eg: software) PMU.
 			 */
 			sub->pmu->read(sub);
+			__perf_read_cgroup_node(sub);
 		}
 	}
 
@@ -4462,6 +4788,10 @@ static void __perf_event_init_context(struct perf_event_context *ctx)
 	INIT_LIST_HEAD(&ctx->pinned_active);
 	INIT_LIST_HEAD(&ctx->flexible_active);
 	refcount_set(&ctx->refcount, 1);
+#ifdef CONFIG_CGROUP_PERF
+	INIT_LIST_HEAD(&ctx->cgrp_ctx_entry);
+	INIT_LIST_HEAD(&ctx->cgrp_node_list);
+#endif
 }
 
 static struct perf_event_context *
@@ -4851,6 +5181,8 @@ static void _free_event(struct perf_event *event)
 	if (is_cgroup_event(event))
 		perf_detach_cgroup(event);
 
+	perf_event_destroy_cgroup_nodes(event);
+
 	if (!event->parent) {
 		if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
 			put_callchain_buffers();
@@ -5571,6 +5903,58 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
 
 		return perf_event_modify_attr(event,  &new_attr);
 	}
+
+	case PERF_EVENT_IOC_ATTACH_CGROUP: {
+		u64 nr_cgrps;
+		u64 *cgrp_buf;
+		size_t cgrp_bufsz;
+		int ret;
+
+		if (!event_can_attach_cgroup(event))
+			return -EINVAL;
+
+		if (copy_from_user(&nr_cgrps, (u64 __user *)arg,
+				   sizeof(nr_cgrps)))
+			return -EFAULT;
+
+		if (nr_cgrps == 0 || nr_cgrps > MAX_CGRP_NODE_HASH)
+			return -EINVAL;
+
+		cgrp_bufsz = nr_cgrps * sizeof(*cgrp_buf);
+
+		cgrp_buf = kmalloc(cgrp_bufsz, GFP_KERNEL);
+		if (cgrp_buf == NULL)
+			return -ENOMEM;
+
+		if (copy_from_user(cgrp_buf, (u64 __user *)(arg + 8),
+				   cgrp_bufsz)) {
+			kfree(cgrp_buf);
+			return -EFAULT;
+		}
+
+		ret = perf_event_attach_cgroup_node(event, nr_cgrps, cgrp_buf);
+
+		kfree(cgrp_buf);
+		return ret;
+	}
+
+	case PERF_EVENT_IOC_READ_CGROUP: {
+		u64 read_size, cgrp_id;
+
+		if (!event_can_attach_cgroup(event))
+			return -EINVAL;
+
+		if (copy_from_user(&read_size, (u64 __user *)arg,
+				   sizeof(read_size)))
+			return -EFAULT;
+		if (copy_from_user(&cgrp_id, (u64 __user *)(arg + 8),
+				   sizeof(cgrp_id)))
+			return -EFAULT;
+
+		return perf_event_read_cgroup_node(event, read_size, cgrp_id,
+						   (char __user *)(arg + 16));
+	}
+
 	default:
 		return -ENOTTY;
 	}
@@ -5583,10 +5967,39 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
 	return 0;
 }
 
+static void perf_sched_enable(void)
+{
+	/*
+	 * We need the mutex here because static_branch_enable()
+	 * must complete *before* the perf_sched_count increment
+	 * becomes visible.
+	 */
+	if (atomic_inc_not_zero(&perf_sched_count))
+		return;
+
+	mutex_lock(&perf_sched_mutex);
+	if (!atomic_read(&perf_sched_count)) {
+		static_branch_enable(&perf_sched_events);
+		/*
+		 * Guarantee that all CPUs observe they key change and
+		 * call the perf scheduling hooks before proceeding to
+		 * install events that need them.
+		 */
+		synchronize_rcu();
+	}
+	/*
+	 * Now that we have waited for the sync_sched(), allow further
+	 * increments to by-pass the mutex.
+	 */
+	atomic_inc(&perf_sched_count);
+	mutex_unlock(&perf_sched_mutex);
+}
+
 static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct perf_event *event = file->private_data;
 	struct perf_event_context *ctx;
+	bool do_sched_enable = false;
 	long ret;
 
 	/* Treat ioctl like writes as it is likely a mutating operation. */
@@ -5595,9 +6008,19 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return ret;
 
 	ctx = perf_event_ctx_lock(event);
+	/* ATTACH_CGROUP requires context switch callback */
+	if (cmd == PERF_EVENT_IOC_ATTACH_CGROUP && !event_has_cgroup_node(event))
+		do_sched_enable = true;
 	ret = _perf_ioctl(event, cmd, arg);
 	perf_event_ctx_unlock(event, ctx);
 
+	/*
+	 * Due to the circular lock dependency, it cannot call
+	 * static_branch_enable() under the ctx->mutex.
+	 */
+	if (do_sched_enable && ret >= 0)
+		perf_sched_enable();
+
 	return ret;
 }
 
@@ -11240,33 +11663,8 @@ static void account_event(struct perf_event *event)
 	if (event->attr.text_poke)
 		atomic_inc(&nr_text_poke_events);
 
-	if (inc) {
-		/*
-		 * We need the mutex here because static_branch_enable()
-		 * must complete *before* the perf_sched_count increment
-		 * becomes visible.
-		 */
-		if (atomic_inc_not_zero(&perf_sched_count))
-			goto enabled;
-
-		mutex_lock(&perf_sched_mutex);
-		if (!atomic_read(&perf_sched_count)) {
-			static_branch_enable(&perf_sched_events);
-			/*
-			 * Guarantee that all CPUs observe they key change and
-			 * call the perf scheduling hooks before proceeding to
-			 * install events that need them.
-			 */
-			synchronize_rcu();
-		}
-		/*
-		 * Now that we have waited for the sync_sched(), allow further
-		 * increments to by-pass the mutex.
-		 */
-		atomic_inc(&perf_sched_count);
-		mutex_unlock(&perf_sched_mutex);
-	}
-enabled:
+	if (inc)
+		perf_sched_enable();
 
 	account_event_cpu(event, event->cpu);
 
@@ -13008,6 +13406,7 @@ static void __init perf_event_init_all_cpus(void)
 
 #ifdef CONFIG_CGROUP_PERF
 		INIT_LIST_HEAD(&per_cpu(cgrp_cpuctx_list, cpu));
+		INIT_LIST_HEAD(&per_cpu(cgroup_ctx_list, cpu));
 #endif
 		INIT_LIST_HEAD(&per_cpu(sched_cb_list, cpu));
 	}
@@ -13218,6 +13617,29 @@ static int perf_cgroup_css_online(struct cgroup_subsys_state *css)
 	return 0;
 }
 
+static int __perf_cgroup_update_node(void *info)
+{
+	struct task_struct *task = info;
+
+	rcu_read_lock();
+	cgroup_node_sched_out(task);
+	rcu_read_unlock();
+
+	return 0;
+}
+
+/* update cgroup counter BEFORE task's cgroup is changed */
+static int perf_cgroup_can_attach(struct cgroup_taskset *tset)
+{
+	struct task_struct *task;
+	struct cgroup_subsys_state *css;
+
+	cgroup_taskset_for_each(task, css, tset)
+		task_function_call(task, __perf_cgroup_update_node, task);
+
+	return 0;
+}
+
 static int __perf_cgroup_move(void *info)
 {
 	struct task_struct *task = info;
@@ -13240,6 +13662,7 @@ struct cgroup_subsys perf_event_cgrp_subsys = {
 	.css_alloc	= perf_cgroup_css_alloc,
 	.css_free	= perf_cgroup_css_free,
 	.css_online	= perf_cgroup_css_online,
+	.can_attach	= perf_cgroup_can_attach,
 	.attach		= perf_cgroup_attach,
 	/*
 	 * Implicitly enable on dfl hierarchy so that perf events can
-- 
2.31.1.295.g9ea45b61b8-goog

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