linux-kernel - Re: [PATCH] LoongArch: Set unwind stack type to unknown rather than set error flag

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Date:   Mon, 27 Nov 2023 10:41:35 +0800
From:   Hengqi Chen <hengqi.chen@...il.com>
To:     Jinyang He <hejinyang@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Set unwind stack type to unknown rather than
 set error flag

On Sun, Nov 26, 2023 at 8:10 PM Jinyang He <hejinyang@...ngson.cn> wrote:
>
> During the unwinding, unwind_done() is used as an end condition. Normally
> it unwind to the user stack and then set the stack type to unknown, which
> is a normal exit. When something unexpected happens in unwind process and
> we cannot unwind anymore, we should set the error flag, and also set the
> stack type to unknown to indicate that the unwind process cannot continue.
> The error flag emphasizes that the unwind process produce an unexpected
> error. There is no unexpected things when we unwind the PT_REGS in the
> top of IRQ stack and find out that is an user mode PT_REGS. Thus, we
> should not set error flag and just set stack type to unknown.
>
> Reported-by: Hengqi Chen <hengqi.chen@...il.com>
> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
> ---
>  arch/loongarch/kernel/stacktrace.c      | 2 +-
>  arch/loongarch/kernel/unwind.c          | 1 -
>  arch/loongarch/kernel/unwind_prologue.c | 2 +-
>  3 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
> index 92270f14db94..f623feb2129f 100644
> --- a/arch/loongarch/kernel/stacktrace.c
> +++ b/arch/loongarch/kernel/stacktrace.c
> @@ -32,7 +32,7 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
>         }
>
>         for (unwind_start(&state, task, regs);
> -            !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) {
> +            !unwind_done(&state); unwind_next_frame(&state)) {
>                 addr = unwind_get_return_address(&state);
>                 if (!addr || !consume_entry(cookie, addr))
>                         break;
> diff --git a/arch/loongarch/kernel/unwind.c b/arch/loongarch/kernel/unwind.c
> index ba324ba76fa1..a463d6961344 100644
> --- a/arch/loongarch/kernel/unwind.c
> +++ b/arch/loongarch/kernel/unwind.c
> @@ -28,6 +28,5 @@ bool default_next_frame(struct unwind_state *state)
>
>         } while (!get_stack_info(state->sp, state->task, info));
>
> -       state->error = true;
>         return false;
>  }
> diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
> index 55afc27320e1..929ae240280a 100644
> --- a/arch/loongarch/kernel/unwind_prologue.c
> +++ b/arch/loongarch/kernel/unwind_prologue.c
> @@ -227,7 +227,7 @@ static bool next_frame(struct unwind_state *state)
>         } while (!get_stack_info(state->sp, state->task, info));
>
>  out:
> -       state->error = true;
> +       state->stack_info.type = STACK_TYPE_UNKNOWN;
>         return false;
>  }
>
> --
> 2.42.0
>

Acked-by: Hengqi Chen <hengqi.chen@...il.com>