[RFC PATCH v1 1/9] timer: fix circular header dependency
Christophe Leroy
christophe.leroy at c-s.fr
Wed Sep 26 03:48:41 AEST 2018
On 09/25/2018 12:15 PM, Christophe LEROY wrote:
>
>
> Le 25/09/2018 à 14:11, Mark Rutland a écrit :
>> On Tue, Sep 25, 2018 at 07:34:15AM +0200, Christophe LEROY wrote:
>>>
>>>
>>> Le 24/09/2018 à 17:52, Christophe Leroy a écrit :
>>>> 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 <christophe.leroy at c-s.fr>
>>>> ---
>>>> 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")
>
> Thanks, I'll have a look
>
>> IIUC, you could do that by placing it in paca_struct.
>
> By the way, it is already in PACA struct for PPC64.
> The issue is with PPC32, up to now it was in current_thread_info:
>
> #ifdef CONFIG_PPC64
> #define raw_smp_processor_id() (local_paca->paca_index)
> #define hard_smp_processor_id() (get_paca()->hw_cpu_id)
> #else
> /* 32-bit */
> extern int smp_hw_index[];
>
> #define raw_smp_processor_id() (current_thread_info()->cpu)
> #define hard_smp_processor_id() (smp_hw_index[smp_processor_id()])
>
> [..]
>
> #endif
>
It seems not that easy. Adding the following leads to the below failure.
I'm having a hard time identifying and fixing the issue. Looks again
like a circular thing, because linux/percpu-defs.h is where
raw_cpu_ptr() is defined.
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -83,7 +83,14 @@ int is_cpu_dead(unsigned int cpu);
/* 32-bit */
extern int smp_hw_index[];
-#define raw_smp_processor_id() (current_thread_info()->cpu)
+DECLARE_PER_CPU_READ_MOSTLY(unsigned int, cpu_number);
+
+/*
+ * We don't use this_cpu_read(cpu_number) as that has implicit writes to
+ * preempt_count, and associated (compiler) barriers, that we'd like to
avoid
+ * the expense of. If we're preemptible, the value can be stale at use
anyway.
+ */
+#define raw_smp_processor_id() (*this_cpu_ptr(&cpu_number))
#define hard_smp_processor_id() (smp_hw_index[smp_processor_id()])
static inline int get_hard_smp_processor_id(int cpu)
CC arch/powerpc/kernel/asm-offsets.s
In file included from ././include/linux/compiler_types.h:64:0,
from <command-line>:0:
./include/linux/percpu-rwsem.h: In function
'percpu_down_read_preempt_disable':
./include/linux/percpu-defs.h:254:27: error: implicit declaration of
function 'raw_cpu_ptr' [-Werror=implicit-function-declaration]
#define this_cpu_ptr(ptr) raw_cpu_ptr(ptr)
^
./include/linux/compiler-gcc.h:58:26: note: in definition of macro
'RELOC_HIDE'
(typeof(ptr)) (__ptr + (off)); \
^
./include/asm-generic/percpu.h:44:31: note: in expansion of macro
'SHIFT_PERCPU_PTR'
#define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
^
./include/asm-generic/percpu.h:31:25: note: in expansion of macro
'per_cpu_offset'
#define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
^
./arch/powerpc/include/asm/smp.h:93:35: note: in expansion of macro
'this_cpu_ptr'
#define raw_smp_processor_id() (*this_cpu_ptr(&cpu_number))
^
./include/asm-generic/percpu.h:31:40: note: in expansion of macro
'raw_smp_processor_id'
#define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
^
./include/asm-generic/percpu.h:44:53: note: in expansion of macro
'__my_cpu_offset'
#define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
^
./include/linux/percpu-defs.h:244:2: note: in expansion of macro
'arch_raw_cpu_ptr'
arch_raw_cpu_ptr(ptr); \
^
./include/asm-generic/percpu.h:76:3: note: in expansion of macro
'raw_cpu_ptr'
*raw_cpu_ptr(&(pcp)) op val; \
^
./include/asm-generic/percpu.h:225:34: note: in expansion of macro
'raw_cpu_generic_to_op'
#define raw_cpu_add_1(pcp, val) raw_cpu_generic_to_op(pcp, val, +=)
^
./include/linux/percpu-defs.h:379:11: note: in expansion of macro
'raw_cpu_add_1'
case 1: stem##1(variable, __VA_ARGS__);break; \
^
./include/linux/percpu-defs.h:424:32: note: in expansion of macro
'__pcpu_size_call'
#define raw_cpu_add(pcp, val) __pcpu_size_call(raw_cpu_add_, pcp, val)
^
./include/linux/percpu-defs.h:460:2: note: in expansion of macro
'raw_cpu_add'
raw_cpu_add(pcp, val); \
^
./include/linux/percpu-defs.h:499:30: note: in expansion of macro
'__this_cpu_add'
#define __this_cpu_inc(pcp) __this_cpu_add(pcp, 1)
^
./include/linux/percpu-rwsem.h:47:2: note: in expansion of macro
'__this_cpu_inc'
__this_cpu_inc(*sem->read_count);
^
./arch/powerpc/include/asm/smp.h:93:34: error: invalid type argument of
unary '*' (have 'int')
#define raw_smp_processor_id() (*this_cpu_ptr(&cpu_number))
^
[...]
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