linux-kernel - [PATCH 1/3] kthread: Remove the flags argument from kernel

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Date:   Sun, 26 Jun 2022 14:15:48 -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 1/3] kthread: Remove the flags argument from kernel_thread


There are only two callers of kernel_thread remaining.  The calling in
init/main.c that creates kthreadd, and the caller in kernel/kthread.c

Both callers pass CLONE_FS|CLONE_FILES.  The argument SIGCHLD causes
terminate to exit with the oridnary process SIGCHLD semantics.

As kthreadd never exists it simply does not matter what kind of exit
it has.  So for simplicity make it look like everything else and use
SIGCHLD.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 include/linux/sched/task.h | 2 +-
 init/main.c                | 2 +-
 kernel/fork.c              | 3 ++-
 kernel/kthread.c           | 2 +-
 4 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 505aaf9fe477..d95930e220da 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, unsigned long flags);
+extern pid_t kernel_thread(int (*fn)(void *), void *arg);
 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 0ee39cdcfcac..211d38db0d16 100644
--- a/init/main.c
+++ b/init/main.c
@@ -701,7 +701,7 @@ 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, NULL);
 	rcu_read_lock();
 	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
 	rcu_read_unlock();
diff --git a/kernel/fork.c b/kernel/fork.c
index 9d44f2d46c69..65909ded0ea7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2694,8 +2694,9 @@ pid_t kernel_clone(struct kernel_clone_args *args)
 /*
  * Create a kernel thread.
  */
-pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
+pid_t kernel_thread(int (*fn)(void *), void *arg)
 {
+	unsigned long flags = CLONE_FS | CLONE_FILES | SIGCHLD;
 	struct kernel_clone_args args = {
 		.flags		= ((lower_32_bits(flags) | CLONE_VM |
 				    CLONE_UNTRACED) & ~CSIGNAL),
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 544fd4097406..c0505e6b7142 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -396,7 +396,7 @@ static void create_kthread(struct kthread_create_info *create)
 	current->pref_node_fork = create->node;
 #endif
 	/* We want our own signal handler (we take no signals by default). */
-	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
+	pid = kernel_thread(kthread, create);
 	if (pid < 0) {
 		/* If user was SIGKILLed, I release the structure. */
 		struct completion *done = xchg(&create->done, NULL);
-- 
2.35.3