The ret_from_kernel_thread() behaves similarly with ret_from_fork(),
the only difference is whether call the fn(arg) or not, this can be
acchieved by testing fn is NULL or not, I.E s0 is 0 or not.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 arch/riscv/kernel/entry.S   | 11 +++--------
 arch/riscv/kernel/process.c |  5 ++---
 2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 2207cf44a3bc..a3e1ed2fa2ac 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -323,20 +323,15 @@ END(handle_kernel_stack_overflow)
 
 ENTRY(ret_from_fork)
 	call schedule_tail
-	move a0, sp /* pt_regs */
-	la ra, ret_from_exception
-	tail syscall_exit_to_user_mode
-ENDPROC(ret_from_fork)
-
-ENTRY(ret_from_kernel_thread)
-	call schedule_tail
+	beqz s0, 1f	/* not from kernel thread */
 	/* Call fn(arg) */
 	move a0, s1
 	jalr s0
+1:
 	move a0, sp /* pt_regs */
 	la ra, ret_from_exception
 	tail syscall_exit_to_user_mode
-ENDPROC(ret_from_kernel_thread)
+ENDPROC(ret_from_fork)
 
 #ifdef CONFIG_IRQ_STACKS
 ENTRY(call_on_stack)
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index ceb9ebab6558..67e7cd123ceb 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -34,7 +34,6 @@ EXPORT_SYMBOL(__stack_chk_guard);
 #endif
 
 extern asmlinkage void ret_from_fork(void);
-extern asmlinkage void ret_from_kernel_thread(void);
 
 void arch_cpu_idle(void)
 {
@@ -172,7 +171,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 		/* Supervisor/Machine, irqs on: */
 		childregs->status = SR_PP | SR_PIE;
 
-		p->thread.ra = (unsigned long)ret_from_kernel_thread;
 		p->thread.s[0] = (unsigned long)args->fn;
 		p->thread.s[1] = (unsigned long)args->fn_arg;
 	} else {
@@ -182,8 +180,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 		if (clone_flags & CLONE_SETTLS)
 			childregs->tp = tls;
 		childregs->a0 = 0; /* Return value of fork() */
-		p->thread.ra = (unsigned long)ret_from_fork;
+		p->thread.s[0] = 0;
 	}
+	p->thread.ra = (unsigned long)ret_from_fork;
 	p->thread.sp = (unsigned long)childregs; /* kernel sp */
 	return 0;
 }
-- 
2.34.1

I would involve this patch in the generic entry series. It would help
remove the ret_from_kernel_thread part in the entry.S.

On Thu, Sep 29, 2022 at 12:29 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> The ret_from_kernel_thread() behaves similarly with ret_from_fork(),
> the only difference is whether call the fn(arg) or not, this can be
> acchieved by testing fn is NULL or not, I.E s0 is 0 or not.
>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  arch/riscv/kernel/entry.S   | 11 +++--------
>  arch/riscv/kernel/process.c |  5 ++---
>  2 files changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 2207cf44a3bc..a3e1ed2fa2ac 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -323,20 +323,15 @@ END(handle_kernel_stack_overflow)
>
>  ENTRY(ret_from_fork)
>         call schedule_tail
> -       move a0, sp /* pt_regs */
> -       la ra, ret_from_exception
> -       tail syscall_exit_to_user_mode
> -ENDPROC(ret_from_fork)
> -
> -ENTRY(ret_from_kernel_thread)
> -       call schedule_tail
> +       beqz s0, 1f     /* not from kernel thread */
>         /* Call fn(arg) */
>         move a0, s1
>         jalr s0
> +1:
>         move a0, sp /* pt_regs */
>         la ra, ret_from_exception
>         tail syscall_exit_to_user_mode
> -ENDPROC(ret_from_kernel_thread)
> +ENDPROC(ret_from_fork)
>
>  #ifdef CONFIG_IRQ_STACKS
>  ENTRY(call_on_stack)
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index ceb9ebab6558..67e7cd123ceb 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -34,7 +34,6 @@ EXPORT_SYMBOL(__stack_chk_guard);
>  #endif
>
>  extern asmlinkage void ret_from_fork(void);
> -extern asmlinkage void ret_from_kernel_thread(void);
>
>  void arch_cpu_idle(void)
>  {
> @@ -172,7 +171,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
>                 /* Supervisor/Machine, irqs on: */
>                 childregs->status = SR_PP | SR_PIE;
>
> -               p->thread.ra = (unsigned long)ret_from_kernel_thread;
>                 p->thread.s[0] = (unsigned long)args->fn;
>                 p->thread.s[1] = (unsigned long)args->fn_arg;
>         } else {
> @@ -182,8 +180,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
>                 if (clone_flags & CLONE_SETTLS)
>                         childregs->tp = tls;
>                 childregs->a0 = 0; /* Return value of fork() */
> -               p->thread.ra = (unsigned long)ret_from_fork;
> +               p->thread.s[0] = 0;
>         }
> +       p->thread.ra = (unsigned long)ret_from_fork;
>         p->thread.sp = (unsigned long)childregs; /* kernel sp */
>         return 0;
>  }
> --
> 2.34.1
>


-- 
Best Regards
 Guo Ren