linux-kernel - [PATCH 4.4 v1 01/17] init: Pin init task to the boot CPU, initially

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Message-Id: <1739170545-25011-2-git-send-email-kazuhiro3.hayashi@toshiba.co.jp>
Date: Mon, 10 Feb 2025 15:55:29 +0900
From: Kazuhiro Hayashi <kazuhiro3.hayashi@...hiba.co.jp>
To: linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
        cip-dev@...ts.cip-project.org
Cc: bigeasy@...utronix.de, tglx@...utronix.de, rostedt@...dmis.org,
        linux-rt-users@...r.kernel.org, pavel@...x.de
Subject: [PATCH 4.4 v1 01/17] init: Pin init task to the boot CPU, initially

From: Thomas Gleixner <tglx@...utronix.de>

commit 8fb12156b8db61af3d49f3e5e104568494581d1f upstream.

Some of the boot code in init_kernel_freeable() which runs before SMP
bringup assumes (rightfully) that it runs on the boot CPU and therefore can
use smp_processor_id() in preemptible context.

That works so far because the smp_processor_id() check starts to be
effective after smp bringup. That's just wrong. Starting with SMP bringup
and the ability to move threads around, smp_processor_id() in preemptible
context is broken.

Aside of that it does not make sense to allow init to run on all CPUs
before sched_smp_init() has been run.

Pin the init to the boot CPU so the existing code can continue to use
smp_processor_id() without triggering the checks when the enabling of those
checks starts earlier.

Tested-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Link: http://lkml.kernel.org/r/20170516184734.943149935@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Kazuhiro Hayashi <kazuhiro3.hayashi@...hiba.co.jp>
---
 init/main.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/init/main.c b/init/main.c
index 9933fca3a5c8..6c745aff6669 100644
--- a/init/main.c
+++ b/init/main.c
@@ -386,6 +386,7 @@ static __initdata DECLARE_COMPLETION(kthreadd_done);
 
 static noinline void __init_refok rest_init(void)
 {
+	struct task_struct *tsk;
 	int pid;
 
 	rcu_scheduler_starting();
@@ -395,7 +396,17 @@ static noinline void __init_refok rest_init(void)
 	 * the init task will end up wanting to create kthreads, which, if
 	 * we schedule it before we create kthreadd, will OOPS.
 	 */
-	kernel_thread(kernel_init, NULL, CLONE_FS);
+	pid = kernel_thread(kernel_init, NULL, CLONE_FS);
+	/*
+	 * Pin init on the boot CPU. Task migration is not properly working
+	 * until sched_init_smp() has been run. It will set the allowed
+	 * CPUs for init to the non isolated CPUs.
+	 */
+	rcu_read_lock();
+	tsk = find_task_by_pid_ns(pid, &init_pid_ns);
+	set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id()));
+	rcu_read_unlock();
+
 	numa_default_policy();
 	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
 	rcu_read_lock();
@@ -993,10 +1004,6 @@ static noinline void __init kernel_init_freeable(void)
 	 * init can allocate pages on any node
 	 */
 	set_mems_allowed(node_states[N_MEMORY]);
-	/*
-	 * init can run on any cpu.
-	 */
-	set_cpus_allowed_ptr(current, cpu_all_mask);
 
 	cad_pid = get_pid(task_pid(current));
 
-- 
2.30.2