linux-kernel - [PATCH 2/3] kthread: Replace kernel_thread with new

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Date:   Sun, 26 Jun 2022 14:16:12 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Christian Brauner <brauner@...nel.org>, Tejun Heo <tj@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>
Subject: [PATCH 2/3] kthread: Replace kernel_thread with new_kthread


It is desriable to be able to perform all of the kthread setup before
the kernel thread is awaked for the first time.

To make that possible replace kernel_thread with new_kthread that does
all of the same work except it does not call wake_up_new_task.

Replace the two uses of kernel_threadd with new_kthread and a call
to wake_up_new_task.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 include/linux/sched/task.h |  2 +-
 init/main.c                |  6 ++----
 kernel/fork.c              |  4 ++--
 kernel/kthread.c           | 10 ++++++----
 4 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index d95930e220da..c4c7a0118553 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -91,7 +91,7 @@ extern pid_t kernel_clone(struct kernel_clone_args *kargs);
 struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node);
 struct task_struct *fork_idle(int);
 struct mm_struct *copy_init_mm(void);
-extern pid_t kernel_thread(int (*fn)(void *), void *arg);
+extern struct task_struct *new_kthread(int (*fn)(void *), void *arg, int node);
 extern pid_t user_mode_thread(int (*fn)(void *), void *arg, unsigned long flags);
 extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
 int kernel_wait(pid_t pid, int *stat);
diff --git a/init/main.c b/init/main.c
index 211d38db0d16..b437581f8001 100644
--- a/init/main.c
+++ b/init/main.c
@@ -701,10 +701,8 @@ noinline void __ref rest_init(void)
 	rcu_read_unlock();
 
 	numa_default_policy();
-	pid = kernel_thread(kthreadd, NULL);
-	rcu_read_lock();
-	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
-	rcu_read_unlock();
+	kthreadd_task = new_kthread(kthreadd, NULL, NUMA_NO_NODE);
+	wake_up_new_task(kthreadd_task);
 
 	/*
 	 * Enable might_sleep() and smp_processor_id() checks.
diff --git a/kernel/fork.c b/kernel/fork.c
index 65909ded0ea7..794d9f9c78bc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2694,7 +2694,7 @@ pid_t kernel_clone(struct kernel_clone_args *args)
 /*
  * Create a kernel thread.
  */
-pid_t kernel_thread(int (*fn)(void *), void *arg)
+struct task_struct *new_kthread(int (*fn)(void *), void *arg, int node)
 {
 	unsigned long flags = CLONE_FS | CLONE_FILES | SIGCHLD;
 	struct kernel_clone_args args = {
@@ -2706,7 +2706,7 @@ pid_t kernel_thread(int (*fn)(void *), void *arg)
 		.kthread	= 1,
 	};
 
-	return kernel_clone(&args);
+	return copy_process(NULL, 0, node, &args);
 }
 
 /*
diff --git a/kernel/kthread.c b/kernel/kthread.c
index c0505e6b7142..8529f6b1582b 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -390,14 +390,14 @@ int tsk_fork_get_node(struct task_struct *tsk)
 
 static void create_kthread(struct kthread_create_info *create)
 {
-	int pid;
+	struct task_struct *new;
 
 #ifdef CONFIG_NUMA
 	current->pref_node_fork = create->node;
 #endif
 	/* We want our own signal handler (we take no signals by default). */
-	pid = kernel_thread(kthread, create);
-	if (pid < 0) {
+	new = new_kthread(kthread, create, NUMA_NO_NODE);
+	if (IS_ERR(new)) {
 		/* If user was SIGKILLed, I release the structure. */
 		struct completion *done = xchg(&create->done, NULL);
 
@@ -405,8 +405,10 @@ static void create_kthread(struct kthread_create_info *create)
 			kfree(create);
 			return;
 		}
-		create->result = ERR_PTR(pid);
+		create->result = ERR_CAST(new);
 		complete(done);
+	} else {
+		wake_up_new_task(new);
 	}
 }
 
-- 
2.35.3