linux-kernel - Re: [PATCH] riscv: Cleanup unnecessary define in asm-offset.c

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Date:   Tue, 21 Jul 2020 18:44:49 -0700 (PDT)
From:   Palmer Dabbelt <palmerdabbelt@...gle.com>
To:     guoren@...nel.org
CC:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-csky@...r.kernel.org, guoren@...nel.org,
        guoren@...ux.alibaba.com
Subject:     Re: [PATCH] riscv: Cleanup unnecessary define in asm-offset.c

On Sun, 12 Jul 2020 06:41:49 PDT (-0700), guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
>
>  - TASK_THREAD_SP is duplicated define
>  - TASK_STACK is no use at all
>  - Don't worry about thread_info's offset in task_struct, have
>    a look on comment in include/linux/sched.h:
>
> struct task_struct {
> 	/*
> 	 * For reasons of header soup (see current_thread_info()), this
> 	 * must be the first element of task_struct.
> 	 */
> 	struct thread_info		thread_info;
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> ---
>  arch/riscv/kernel/asm-offsets.c | 3 ---
>  arch/riscv/kernel/entry.S       | 5 -----
>  2 files changed, 8 deletions(-)
>
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index 07cb9c1..db20344 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -27,9 +27,6 @@ void asm_offsets(void)
>  	OFFSET(TASK_THREAD_S9, task_struct, thread.s[9]);
>  	OFFSET(TASK_THREAD_S10, task_struct, thread.s[10]);
>  	OFFSET(TASK_THREAD_S11, task_struct, thread.s[11]);
> -	OFFSET(TASK_THREAD_SP, task_struct, thread.sp);
> -	OFFSET(TASK_STACK, task_struct, stack);
> -	OFFSET(TASK_TI, task_struct, thread_info);
>  	OFFSET(TASK_TI_FLAGS, task_struct, thread_info.flags);
>  	OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count);
>  	OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index cae7e6d..3e8707e 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -389,12 +389,7 @@ ENTRY(__switch_to)
>  	lw a4, TASK_TI_CPU(a1)
>  	sw a3, TASK_TI_CPU(a1)
>  	sw a4, TASK_TI_CPU(a0)
> -#if TASK_TI != 0
> -#error "TASK_TI != 0: tp will contain a 'struct thread_info', not a 'struct task_struct' so get_current() won't work."
> -	addi tp, a1, TASK_TI
> -#else
>  	move tp, a1
> -#endif

Seems reasonable.  That was really there to save anyone who got bit by the
conversion to to THREAD_INFO_IN_TASK.

I've added a comment and put this on for-next.

Thanks!

>  	ret
>  ENDPROC(__switch_to)

Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>