linux-kernel - Re: [RFC PATCH 7/8] riscv: rely on core code to keep thread

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Message-ID: <mhng-7d24dba9-38a7-4267-b01c-388471412237@palmerdabbelt-glaptop>
Date:   Tue, 28 Sep 2021 15:07:39 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     ardb@...nel.org
CC:     linux-kernel@...r.kernel.org, ardb@...nel.org, keithpac@...zon.com,
        linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        mpe@...erman.id.au, benh@...nel.crashing.org,
        christophe.leroy@...roup.eu, paulus@...ba.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, hca@...ux.ibm.com, gor@...ux.ibm.com,
        borntraeger@...ibm.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, peterz@...radead.org, keescook@...omium.org,
        luto@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org
Subject:     Re: [RFC PATCH 7/8] riscv: rely on core code to keep thread_info::cpu updated

On Tue, 14 Sep 2021 05:10:35 PDT (-0700), ardb@...nel.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@...nel.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@...gle.com>

Thanks!