[patch 01/18] init: Pin init task to boot cpu initially

[Thomas Gleixner]

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@xxxxxxxxxxxxx>
---
 init/main.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/init/main.c
+++ b/init/main.c
@@ -1015,10 +1015,13 @@ 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.
+	 * 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.
 	 */
-	set_cpus_allowed_ptr(current, cpu_all_mask);
+	set_cpus_allowed_ptr(current, cpumask_of(raw_smp_processor_id()));
 
 	cad_pid = task_pid(current);