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Date:   Fri,  1 May 2020 12:01:51 -0400
From:   "J. Bruce Fields" <bfields@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-nfs@...r.kernel.org, Jeff Layton <jlayton@...hat.com>,
        David Howells <dhowells@...hat.com>, Tejun Heo <tj@...nel.org>,
        Shaohua Li <shli@...com>, Oleg Nesterov <oleg@...hat.com>,
        linux-kernel@...r.kernel.org,
        "J. Bruce Fields" <bfields@...hat.com>
Subject: [PATCH 3/4] kthreads: allow multiple kthreadd's

From: "J. Bruce Fields" <bfields@...hat.com>

Allow subsystems to run their own kthreadd's.

I'm experimenting with this to allow nfsd to put its threads into its
own thread group to make it easy for the vfs to tell when nfsd is
breaking one of its own leases.

Signed-off-by: J. Bruce Fields <bfields@...hat.com>
---
 include/linux/kthread.h |  20 ++++++-
 init/main.c             |   4 +-
 kernel/kthread.c        | 113 ++++++++++++++++++++++++++++++----------
 3 files changed, 107 insertions(+), 30 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 8bbcaad7ef0f..a7ffdf96a3b2 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -5,6 +5,24 @@
 #include <linux/err.h>
 #include <linux/sched.h>
 
+struct kthread_group {
+	char *name;
+	spinlock_t create_lock;
+	struct list_head create_list;
+	struct task_struct *task;
+};
+
+extern struct kthread_group kthreadd_default;
+
+struct kthread_group *kthread_start_group(char *);
+void kthread_stop_group(struct kthread_group *);
+
+struct task_struct *kthread_group_create_on_node(struct kthread_group *,
+					int (*threadfn)(void *data),
+					 void *data,
+					 int node,
+					 const char namefmt[], ...);
+
 __printf(4, 5)
 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 					   void *data,
@@ -63,7 +81,7 @@ int kthread_park(struct task_struct *k);
 void kthread_unpark(struct task_struct *k);
 void kthread_parkme(void);
 
-int kthreadd(void *unused);
+int kthreadd(void *);
 extern struct task_struct *kthreadd_task;
 extern int tsk_fork_get_node(struct task_struct *tsk);
 
diff --git a/init/main.c b/init/main.c
index a48617f2e5e5..5256071b0e05 100644
--- a/init/main.c
+++ b/init/main.c
@@ -641,9 +641,9 @@ noinline void __ref rest_init(void)
 	rcu_read_unlock();
 
 	numa_default_policy();
-	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
+	pid = kernel_thread(kthreadd, &kthreadd_default, CLONE_FS | CLONE_FILES);
 	rcu_read_lock();
-	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
+	kthreadd_default.task = find_task_by_pid_ns(pid, &init_pid_ns);
 	rcu_read_unlock();
 
 	/*
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 483bee57a9c8..5232f6f597b5 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -25,9 +25,44 @@
 #include <linux/numa.h>
 #include <trace/events/sched.h>
 
-static DEFINE_SPINLOCK(kthread_create_lock);
-static LIST_HEAD(kthread_create_list);
-struct task_struct *kthreadd_task;
+struct kthread_group kthreadd_default = {
+	.name = "kthreadd",
+	.create_lock = __SPIN_LOCK_UNLOCKED(kthreadd_default.create_lock),
+	.create_list = LIST_HEAD_INIT(kthreadd_default.create_list),
+};
+
+void wake_kthreadd(struct kthread_group *kg)
+{
+	wake_up_process(kg->task);
+}
+
+struct kthread_group *kthread_start_group(char *name)
+{
+	struct kthread_group *new;
+	struct task_struct *task;
+
+	new = kmalloc(sizeof(struct kthread_group), GFP_KERNEL);
+	if (!new)
+		return ERR_PTR(-ENOMEM);
+	spin_lock_init(&new->create_lock);
+	INIT_LIST_HEAD(&new->create_list);
+	new->name = name;
+	task = kthread_run(kthreadd, new, name);
+	if (IS_ERR(task)) {
+		kfree(new);
+		return ERR_CAST(task);
+	}
+	new->task = task;
+	return new;
+}
+EXPORT_SYMBOL_GPL(kthread_start_group);
+
+void kthread_stop_group(struct kthread_group *kg)
+{
+	kthread_stop(kg->task);
+	kfree(kg);
+}
+EXPORT_SYMBOL_GPL(kthread_stop_group);
 
 struct kthread_create_info
 {
@@ -301,11 +336,13 @@ static void create_kthread(struct kthread_create_info *create)
 	}
 }
 
-static __printf(4, 0)
-struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
-						    void *data, int node,
-						    const char namefmt[],
-						    va_list args)
+
+static __printf(5, 0)
+struct task_struct *__kthread_group_create_on_node(struct kthread_group *kg,
+						int (*threadfn)(void *data),
+						void *data, int node,
+						const char namefmt[],
+						va_list args)
 {
 	DECLARE_COMPLETION_ONSTACK(done);
 	struct task_struct *task;
@@ -319,11 +356,11 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 	create->node = node;
 	create->done = &done;
 
-	spin_lock(&kthread_create_lock);
-	list_add_tail(&create->list, &kthread_create_list);
-	spin_unlock(&kthread_create_lock);
+	spin_lock(&kg->create_lock);
+	list_add_tail(&create->list, &kg->create_list);
+	spin_unlock(&kg->create_lock);
 
-	wake_up_process(kthreadd_task);
+	wake_kthreadd(kg);
 	/*
 	 * Wait for completion in killable state, for I might be chosen by
 	 * the OOM killer while kthreadd is trying to allocate memory for
@@ -365,6 +402,25 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 	return task;
 }
 
+__printf(5, 0)
+struct task_struct *kthread_group_create_on_node(struct kthread_group *kg,
+						int (*threadfn)(void *data),
+						void *data, int node,
+						const char namefmt[],
+						...)
+{
+	struct task_struct *task;
+	va_list args;
+
+	va_start(args, namefmt);
+	task = __kthread_group_create_on_node(kg, threadfn,
+						data, node, namefmt, args);
+	va_end(args);
+
+	return task;
+}
+EXPORT_SYMBOL_GPL(kthread_group_create_on_node);
+
 /**
  * kthread_create_on_node - create a kthread.
  * @threadfn: the function to run until signal_pending(current).
@@ -397,7 +453,8 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 	va_list args;
 
 	va_start(args, namefmt);
-	task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
+	task = __kthread_group_create_on_node(&kthreadd_default, threadfn,
+						data, node, namefmt, args);
 	va_end(args);
 
 	return task;
@@ -577,30 +634,31 @@ int kthread_stop(struct task_struct *k)
 }
 EXPORT_SYMBOL(kthread_stop);
 
-void kthread_do_work(void)
+void kthread_do_work(struct kthread_group *kg)
 {
-	spin_lock(&kthread_create_lock);
-	while (!list_empty(&kthread_create_list)) {
+	spin_lock(&kg->create_lock);
+	while (!list_empty(&kg->create_list)) {
 		struct kthread_create_info *create;
 
-		create = list_entry(kthread_create_list.next,
+		create = list_entry(kg->create_list.next,
 				    struct kthread_create_info, list);
 		list_del_init(&create->list);
-		spin_unlock(&kthread_create_lock);
+		spin_unlock(&kg->create_lock);
 
 		create_kthread(create);
 
-		spin_lock(&kthread_create_lock);
+		spin_lock(&kg->create_lock);
 	}
-	spin_unlock(&kthread_create_lock);
+	spin_unlock(&kg->create_lock);
 }
 
-int kthreadd(void *unused)
+int kthreadd(void *data)
 {
+	struct kthread_group *kg = data;
 	struct task_struct *tsk = current;
 
 	/* Setup a clean context for our children to inherit. */
-	set_task_comm(tsk, "kthreadd");
+	set_task_comm(tsk, kg->name);
 	ignore_signals(tsk);
 	set_cpus_allowed_ptr(tsk, cpu_all_mask);
 	set_mems_allowed(node_states[N_MEMORY]);
@@ -608,13 +666,13 @@ int kthreadd(void *unused)
 	current->flags |= PF_NOFREEZE;
 	cgroup_init_kthreadd();
 
-	for (;;) {
+	while (current == kthreadd_default.task || !kthread_should_stop()) {
 		set_current_state(TASK_INTERRUPTIBLE);
-		if (list_empty(&kthread_create_list))
+		if (list_empty(&kg->create_list))
 			schedule();
 		__set_current_state(TASK_RUNNING);
 
-		kthread_do_work();
+		kthread_do_work(kg);
 	}
 
 	return 0;
@@ -712,8 +770,9 @@ __kthread_create_worker(int cpu, unsigned int flags,
 	if (cpu >= 0)
 		node = cpu_to_node(cpu);
 
-	task = __kthread_create_on_node(kthread_worker_fn, worker,
-						node, namefmt, args);
+	task = __kthread_group_create_on_node(&kthreadd_default,
+					kthread_worker_fn,
+					worker, node, namefmt, args);
 	if (IS_ERR(task))
 		goto fail_task;
 
-- 
2.26.2

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