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

Thomas Gleixner
2017-05-16T18:52:36Z

[-- Attachment #1: init--Pin-init-task-to-boot-cpu-initially.patch --]
[-- Type: text/plain, Size: 2087 bytes --]

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);