linux-kernel - Re: [PATCH V3] riscv: patch_text: Fixup last cpu should be master

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Date:   Thu, 21 Apr 2022 15:57:32 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     guoren@...nel.org
CC:     guoren@...nel.org, Arnd Bergmann <arnd@...db.de>,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, guoren@...ux.alibaba.com,
        mhiramat@...nel.org, stable@...r.kernel.org
Subject:     Re: [PATCH V3] riscv: patch_text: Fixup last cpu should be master

On Wed, 06 Apr 2022 07:16:49 PDT (-0700), guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
>
> These patch_text implementations are using stop_machine_cpuslocked
> infrastructure with atomic cpu_count. The original idea: When the
> master CPU patch_text, the others should wait for it. But current
> implementation is using the first CPU as master, which couldn't
> guarantee the remaining CPUs are waiting. This patch changes the
> last CPU as the master to solve the potential risk.
>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> Acked-by: Palmer Dabbelt <palmer@...osinc.com>
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: <stable@...r.kernel.org>
> ---
>  arch/riscv/kernel/patch.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 0b552873a577..765004b60513 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -104,7 +104,7 @@ static int patch_text_cb(void *data)
>  	struct patch_insn *patch = data;
>  	int ret = 0;
>
> -	if (atomic_inc_return(&patch->cpu_count) == 1) {
> +	if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
>  		ret =
>  		    patch_text_nosync(patch->addr, &patch->insn,
>  					    GET_INSN_LENGTH(patch->insn));

Thanks, this is on fixes.