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

tip-bot for Thomas Gleixner
2017-05-23T08:52:25Z

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);