[RFC PATCH 7/8] riscv: rely on core code to keep thread_info::cpu updated

[Palmer Dabbelt]

On Tue, 14 Sep 2021 05:10:35 PDT (-0700), ardb at kernel.org wrote:
> Now that the core code switched back to using thread_info::cpu to keep
> a task's CPU number, we no longer need to keep it in sync explicitly. So
> just drop the code that does this.
>
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
>  arch/riscv/kernel/asm-offsets.c | 1 -
>  arch/riscv/kernel/entry.S       | 5 -----
>  arch/riscv/kernel/head.S        | 1 -
>  3 files changed, 7 deletions(-)
>
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index 90f8ce64fa6f..478d9f02dab5 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -33,7 +33,6 @@ void asm_offsets(void)
>  	OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count);
>  	OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);
>  	OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp);
> -	OFFSET(TASK_TI_CPU, task_struct, thread_info.cpu);
>
>  	OFFSET(TASK_THREAD_F0,  task_struct, thread.fstate.f[0]);
>  	OFFSET(TASK_THREAD_F1,  task_struct, thread.fstate.f[1]);
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 98f502654edd..459eb1714353 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -544,11 +544,6 @@ ENTRY(__switch_to)
>  	REG_L s9,  TASK_THREAD_S9_RA(a4)
>  	REG_L s10, TASK_THREAD_S10_RA(a4)
>  	REG_L s11, TASK_THREAD_S11_RA(a4)
> -	/* Swap the CPU entry around. */
> -	lw a3, TASK_TI_CPU(a0)
> -	lw a4, TASK_TI_CPU(a1)
> -	sw a3, TASK_TI_CPU(a1)
> -	sw a4, TASK_TI_CPU(a0)
>  	/* The offset of thread_info in task_struct is zero. */
>  	move tp, a1
>  	ret
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index fce5184b22c3..d5ec30ef6f5d 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -317,7 +317,6 @@ clear_bss_done:
>  	call setup_trap_vector
>  	/* Restore C environment */
>  	la tp, init_task
> -	sw zero, TASK_TI_CPU(tp)
>  	la sp, init_thread_union + THREAD_SIZE
>
>  #ifdef CONFIG_KASAN

Acked-by: Palmer Dabbelt <palmerdabbelt at google.com>

Thanks!