On Tue, Sep 25, 2018 at 07:34:15AM +0200, Christophe LEROY wrote:

Le 24/09/2018 à 17:52, Christophe Leroy a écrit :

quoted

When switching powerpc to CONFIG_THREAD_INFO_IN_TASK, include/sched.h
has to be included in asm/smp.h for the following change, in order
to avoid uncomplete definition of task_struct:

-#define raw_smp_processor_id() (current_thread_info()->cpu)
+#define raw_smp_processor_id() (current->cpu)

But this generates the following compilation error, due to circular
header dependency.

   CC      kernel/time/alarmtimer.o
In file included from ./arch/powerpc/include/asm/smp.h:31,
                  from ./include/linux/smp.h:64,
                  from ./include/linux/percpu.h:7,
                  from ./include/linux/hrtimer.h:22,
                  from kernel/time/alarmtimer.c:19:
./include/linux/sched.h:558:19: error: field 'dl_timer' has incomplete type
   struct hrtimer   dl_timer;
                    ^~~~~~~~
./include/linux/sched.h:567:17: error: field 'inactive_timer' has incomplete type
   struct hrtimer inactive_timer;
                  ^~~~~~~~~~~~~~
make[1]: *** [kernel/time/alarmtimer.o] Error 1
make: *** [kernel/time/alarmtimer.o] Error 2

   CC      fs/timerfd.o
In file included from ./arch/powerpc/include/asm/smp.h:31,
                  from ./include/linux/smp.h:64,
                  from ./include/linux/percpu.h:7,
                  from ./include/linux/hrtimer.h:22,
                  from ./include/linux/alarmtimer.h:6,
                  from fs/timerfd.c:12:
./include/linux/sched.h:558:19: error: field 'dl_timer' has incomplete type
   struct hrtimer   dl_timer;
                    ^~~~~~~~
./include/linux/sched.h:567:17: error: field 'inactive_timer' has incomplete type
   struct hrtimer inactive_timer;
                  ^~~~~~~~~~~~~~
make[1]: *** [fs/timerfd.o] Error 1
make: *** [fs/timerfd.o] Error 2

This patch fixes it by including linux/hrtimer.h after linux/sched.h

Signed-off-by: Christophe Leroy <redacted>
---
  Should it be fixed in powerpc instead ? In that case, how ? Any idea ?

Looks like there are several other places where the problem occurs, so it
has to be fixed in the powerpc headers instead.

Seems like RISC arch faced the same issue, and fixed it the following way:

/*
 * This is particularly ugly: it appears we can't actually get the
definition
 * of task_struct here, but we need access to the CPU this task is running
on.
 * Instead of using C we're using asm-offsets.h to get the current processor
 * ID.
 */
#define raw_smp_processor_id() (*((int*)((char*)get_current() +
TASK_TI_CPU)))


Unless someone has a better idea, I'll fixed it that way.

To solve this on arm64 we made the cpu number a percpu variable; see
commit:

  57c82954e77fa12c ("arm64: make cpu number a percpu variable")

IIUC, you could do that by placing it in paca_struct.

Thanks,
Mark.