Re: [PATCH 3/4] LoongArch: Add stacktrace support

[zhangqing <zhangqing@loongson.cn>]

On 2022/8/1 下午11:30, Huacai Chen wrote:
> Hi, Qing,
> 
> On Mon, Aug 1, 2022 at 8:17 PM Qing Zhang <zhangqing@loongson.cn> wrote:
>>
>> Use common arch_stack_walk infrastructure to avoid duplicated code and
>> avoid taking care of the stack storage and filtering.
>> Add sra (means __schedule return address) and scfa (means __schedule call
>> frame address) to thread_info and store it in switch_to().
>>
>> Now we can print the process stack by cat /proc/*/stack and can better
>> support ftrace.
>>
>> Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
>> ---
>>   arch/loongarch/Kconfig                 |  5 ++++
>>   arch/loongarch/include/asm/processor.h |  9 +++++++
>>   arch/loongarch/include/asm/switch_to.h | 14 ++++++----
>>   arch/loongarch/include/asm/uaccess.h   |  4 +--
>>   arch/loongarch/kernel/Makefile         |  1 +
>>   arch/loongarch/kernel/asm-offsets.c    |  2 ++
>>   arch/loongarch/kernel/process.c        |  3 +++
>>   arch/loongarch/kernel/stacktrace.c     | 37 ++++++++++++++++++++++++++
>>   arch/loongarch/kernel/switch.S         |  2 ++
>>   9 files changed, 70 insertions(+), 7 deletions(-)
>>   create mode 100644 arch/loongarch/kernel/stacktrace.c
>>
>> diff --git a/arch/loongarch/include/asm/uaccess.h b/arch/loongarch/include/asm/uaccess.h
>> index 2b44edc604a2..a8ae2af4025a 100644
>> --- a/arch/loongarch/include/asm/uaccess.h
>> +++ b/arch/loongarch/include/asm/uaccess.h
>> @@ -229,13 +229,13 @@ extern unsigned long __copy_user(void *to, const void *from, __kernel_size_t n);
>>   static inline unsigned long __must_check
>>   raw_copy_from_user(void *to, const void __user *from, unsigned long n)
>>   {
>> -       return __copy_user(to, from, n);
>> +       return __copy_user(to, (__force const void *)from, n);
>>   }
>>
>>   static inline unsigned long __must_check
>>   raw_copy_to_user(void __user *to, const void *from, unsigned long n)
>>   {
>> -       return __copy_user(to, from, n);
>> +       return __copy_user((__force void *)to, from, n);
> Why this? Does it have something to do with stacktrace?
> 
> Huacai

Hi, huacai

This is kernel test robot report sparse warnings:
I reproduced locally and found that other architectures calling 
__copy_user also use __force conversion, Is this modification appropriate?

kernel/trace/trace_events_user.c: note: in included file (through 
include/linux/uaccess.h, include/linux/sched/task.h, 
include/linux/sched/signal.h, ...):
    arch/loongarch/include/asm/uaccess.h:232:32: sparse: sparse: 
incorrect type in argument 2 (different address spaces) @@     expected 
void const *from @@     got void const [noderef] __user *from @@
    arch/loongarch/include/asm/uaccess.h:232:32: sparse:     expected 
void const *from
    arch/loongarch/include/asm/uaccess.h:232:32: sparse:     got void 
const [noderef] __user *from

Thanks,
-Qing