linux-kernel - Re: [PATCH v1] LoongArch: Remove unnecessary checks in bt

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Message-ID: <a1674623-4c08-1f4d-3e4e-5511b579e9ea@loongson.cn>
Date: Wed, 10 Dec 2025 16:00:02 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] LoongArch: Remove unnecessary checks in bt_address()

On 2025/12/10 上午10:25, Bibo Mao wrote:
> 
> 
> On 2025/12/10 上午9:28, Tiezhu Yang wrote:
>> On 2025/12/9 下午4:30, Huacai Chen wrote:
>>> Hi, Tiezhu,
>>>
>>> On Tue, Dec 9, 2025 at 2:18 PM Tiezhu Yang <yangtiezhu@...ngson.cn> 
>>> wrote:
>>>>
>> ...
>>>>          extern unsigned long eentry;
>>>>
>>>> -       if (__kernel_text_address(ra))
>>>> -               return ra;
>>>> -
>>>> -       if (__module_text_address(ra))
>>>> -               return ra;
>>> I think the correct way is to remove the __module_text_address()
>>> condition but keep the __kernel_text_address() condition. Then return
>>> 0 at the end of this function, and remove the __kernel_text_address()
>>> condition out of this function.
>>
>> It can not remove the check of __kernel_text_address() after calling
>> bt_address() because it needs to validate the calculated address for
>> exception, then no need to keep the __kernel_text_address() condition
>> in bt_address() because it will check the PC outside bt_address().
>          state->pc = bt_address(pc);
>          if (!state->pc) {
>                  pr_err("cannot find unwind pc at %p\n", (void *)pc);
>                  goto err;
>          }
> 
>          if (!__kernel_text_address(state->pc))
>                  goto err;
> I guess that you both comes from different views :) one treats these 
> piece of code into one, one only views function bt_address().
> 
> Especially with if (!state->pc), how could this happen?

IMO, state->pc will be not 0 forever in practice, this check is just an
error path and can be removed too if possible.

Thanks,
Tiezhu