On Tue, 16 May 2017 20:42:32 +0200 Thomas Gleixner <[email protected]> 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 <[email protected]> > --- > 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); > >
