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[patch V2 01/17] init: Pin init task to boot cpu initially

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  [patch V2 01/17] init: Pin init task to boot cpu initially Thomas Gleixner <tglx@linutronix.de> - 2017-05-16 21:00 +0200
    Re: [patch V2 01/17] init: Pin init task to boot cpu initially Steven Rostedt <rostedt@goodmis.org> - 2017-05-16 21:10 +0200
    [tip:sched/core] init: Pin init task to the boot CPU, initially tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-05-23 11:00 +0200

#1642758 — [patch V2 01/17] init: Pin init task to boot cpu initially

Some of the boot code in init_kernel_freeable() which runs before SMP
bringup assumes (rightfully) that it runs on the boot cpu and therefor 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.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 init/main.c |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

--- a/init/main.c
+++ b/init/main.c
@@ -389,6 +389,7 @@ static __initdata DECLARE_COMPLETION(kth
 
 static noinline void __ref rest_init(void)
 {
+	struct task_struct *tsk;
 	int pid;
 
 	rcu_scheduler_starting();
@@ -397,7 +398,17 @@ static noinline void __ref rest_init(voi
 	 * 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();
@@ -1015,10 +1026,6 @@ static noinline void __init kernel_init_
 	 * 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 = task_pid(current);
 

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#1642770

On Tue, 16 May 2017 20:42:32 +0200
Thomas Gleixner <tglx@linutronix.de> wrote:

> Some of the boot code in init_kernel_freeable() which runs before SMP
> bringup assumes (rightfully) that it runs on the boot cpu and therefor 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.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  init/main.c |   17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> --- a/init/main.c
> +++ b/init/main.c
> @@ -389,6 +389,7 @@ static __initdata DECLARE_COMPLETION(kth
>  
>  static noinline void __ref rest_init(void)
>  {
> +	struct task_struct *tsk;
>  	int pid;
>  
>  	rcu_scheduler_starting();
> @@ -397,7 +398,17 @@ static noinline void __ref rest_init(voi
>  	 * 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);

Should we have a:

	BUG_ON(!tsk);

Just to be paranoid?

-- Steve

> +	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();
> @@ -1015,10 +1026,6 @@ static noinline void __init kernel_init_
>  	 * 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 = task_pid(current);
>  
> 

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#1647851 — [tip:sched/core] init: Pin init task to the boot CPU, initially

Commit-ID:  8fb12156b8db61af3d49f3e5e104568494581d1f
Gitweb:     http://git.kernel.org/tip/8fb12156b8db61af3d49f3e5e104568494581d1f
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 16 May 2017 20:42:32 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 23 May 2017 10:01:34 +0200

init: Pin init task to the boot CPU, initially

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@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170516184734.943149935@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 init/main.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/init/main.c b/init/main.c
index f866510..badae3b 100644
--- a/init/main.c
+++ b/init/main.c
@@ -389,6 +389,7 @@ static __initdata DECLARE_COMPLETION(kthreadd_done);
 
 static noinline void __ref rest_init(void)
 {
+	struct task_struct *tsk;
 	int pid;
 
 	rcu_scheduler_starting();
@@ -397,7 +398,17 @@ static noinline void __ref 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();
@@ -1015,10 +1026,6 @@ 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 = task_pid(current);
 

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