[RFC PATCH riscv/for-next 4/4] riscv: ftrace: do not use stop_machine to update code

[Palmer Dabbelt]

On Sun, 29 May 2022 07:33:15 PDT (-0700), andy.chiu at sifive.com wrote:
> Now it is safe to remove dependency from stop_machine() to patch code in
> ftrace.
>
> Signed-off-by: Andy Chiu <andy.chiu at sifive.com>
> Reviewed-by: Greentime Hu <greentime.hu at sifive.com>
> Reviewed-by: Zong Li <zong.li at sifive.com>
> ---
>  arch/riscv/kernel/ftrace.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index d4bf0e5255f6..e7b8bf0a699b 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -12,6 +12,11 @@
>  #include <asm/patch.h>
>
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +void arch_ftrace_update_code(int command)
> +{
> +	ftrace_modify_all_code(command);
> +}
> +
>  int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
>  {
>  	mutex_lock(&text_mutex);

Reviewed-by: Palmer Dabbelt <palmer at rivosinc.com>

Assuming we sort out the issues in #3.  IIUC we don't need to ensure the 
command is fully visible before returning, as the concurrent 
modification scheme doesn't flush the remote icaches and thus may skip 
instrumentation.