linux-kernel - [PATCH 6/7] fork: Explicitly set PF

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Date:   Fri,  6 May 2022 09:15:11 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-arch@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Al Viro <viro@...IV.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 6/7] fork: Explicitly set PF_KTHREAD

Instead of implicitly inheriting PF_KTHREAD from the parent process
examine arguments in kernel_clone_args to see if PF_KTHREAD should be
set.  This makes knowledge of which new threads are kernel threads
explicit.

This also makes it so that init and the user mode helper processes
no longer have PF_KTHREAD set.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/fork.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 8e17c3fbce42..35645f57bd2f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2068,6 +2068,9 @@ static __latent_entropy struct task_struct *copy_process(
 	p = dup_task_struct(current, node);
 	if (!p)
 		goto fork_out;
+	p->flags &= ~PF_KTHREAD;
+	if (args->kthread)
+		p->flags |= PF_KTHREAD;
 	if (args->io_thread) {
 		/*
 		 * Mark us an IO worker, and block any signal that isn't
-- 
2.35.3