Re: [rcu:rcu:smp:hotplug 3/6] softirq.c:(.init.text+0x540): undefined reference to `smpboot_register

[Fengguang Wu <fengguang.wu@intel.com>]

> > kernel/built-in.o: In function `spawn_ksoftirqd':
> > softirq.c:(.init.text+0x540): undefined reference to `smpboot_register_percpu_thread'
> 
> Hello, Fengguang,
> 
> Does the following patch help?

Yeah, it helps!

Thanks,
Fengguang

> ------------------------------------------------------------------------
> 
> 
> hotplug: Fix UP bug in smpboot hotplug code
> 
> Because kernel subsystems need their per-CPU kthreads on UP systems
> as well as on SMP systems, the smpboot hotplug kthread functions
> must be provided in UP builds as well as in SMP builds.  This commit
> therefore adds smpboot.c to UP builds and excludes irrelevant code
> via #ifdef.
> 
> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> diff --git a/kernel/Makefile b/kernel/Makefile
> index c0cc67a..e5602d3 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -10,7 +10,7 @@ obj-y     = fork.o exec_domain.o panic.o printk.o \
>  	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
>  	    hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
>  	    notifier.o ksysfs.o cred.o \
> -	    async.o range.o groups.o lglock.o
> +	    async.o range.o groups.o lglock.o smpboot.o
>  
>  ifdef CONFIG_FUNCTION_TRACER
>  # Do not trace debug files and internal ftrace files
> @@ -46,7 +46,6 @@ obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o
>  obj-$(CONFIG_RT_MUTEX_TESTER) += rtmutex-tester.o
>  obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
>  obj-$(CONFIG_SMP) += smp.o
> -obj-$(CONFIG_SMP) += smpboot.o
>  ifneq ($(CONFIG_SMP),y)
>  obj-y += up.o
>  endif
> diff --git a/kernel/smpboot.c b/kernel/smpboot.c
> index e17653d..6b0d6fe 100644
> --- a/kernel/smpboot.c
> +++ b/kernel/smpboot.c
> @@ -15,6 +15,8 @@
>  
>  #include "smpboot.h"
>  
> +#ifdef CONFIG_SMP
> +
>  #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
>  /*
>   * For the hotplug case we keep the task structs around and reuse
> @@ -67,6 +69,8 @@ void __init idle_threads_init(void)
>  }
>  #endif
>  
> +#endif /* #ifdef CONFIG_SMP */
> +
>  static LIST_HEAD(hotplug_threads);
>  static DEFINE_MUTEX(smpboot_threads_lock);
>