Re: [PATCH] kthread: kthread_bind fails to enforce CPU affinity (fixes kernel BUG at kernel/smpboot.c:134!)

Hi Linus,

The __set_task_cpu() function does various other things too:

        set_task_rq(p, cpu);
  #ifdef CONFIG_SMP
        /*
         * After ->cpu is set up to a new value, task_rq_lock(p, ...)
can be
         * successfuly executed on another CPU. We must ensure that
updates of
         * per-task data have been completed by this moment.
         */
        smp_wmb();
        task_thread_info(p)->cpu = cpu;
        p->wake_cpu = cpu;
  #endif

which makes me worry about just setting the thread_info->cpu value.
That set_task_rq() initializes various group scheduling things, an
dthat whole "wake_cpu" thing seems relevant too.

Yeah, I would definitely like the scheduler guys to weigh in on this,
especially considering how difficult it can be to hit.

Anton