Commit 8fb12156 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar

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: default avatarMark Rutland <>
Signed-off-by: default avatarThomas Gleixner <>
Signed-off-by: default avatarPeter Zijlstra (Intel) <>
Cc: Greg Kroah-Hartman <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Steven Rostedt <>
Link: default avatarIngo Molnar <>
parent 8655d549
......@@ -389,6 +389,7 @@ static __initdata DECLARE_COMPLETION(kthreadd_done);
static noinline void __ref rest_init(void)
struct task_struct *tsk;
int pid;
......@@ -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.
tsk = find_task_by_pid_ns(pid, &init_pid_ns);
set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id()));
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
......@@ -1015,10 +1026,6 @@ static noinline void __init kernel_init_freeable(void)
* init can allocate pages on any node
* init can run on any cpu.
set_cpus_allowed_ptr(current, cpu_all_mask);
cad_pid = task_pid(current);
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