linux-kernel - Re: [PATCH v1 2/2] LoongArch: Return 0 for user tasks in arch_stack_walk

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Message-ID: <47be74ad-c01c-cf79-b7a4-3f05f85c2f71@loongson.cn>
Date: Mon, 15 Sep 2025 16:54:47 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Jinyang He <hejinyang@...ngson.cn>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Huacai Chen
 <chenhuacai@...nel.org>, Xi Zhang <zhangxi@...inos.cn>,
 live-patching@...r.kernel.org, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] LoongArch: Return 0 for user tasks in
 arch_stack_walk_reliable()

On 2025/9/12 上午9:55, Jinyang He wrote:
> On 2025-09-11 19:49, Tiezhu Yang wrote:
> 
>> On 2025/9/10 上午9:11, Jinyang He wrote:
>>> On 2025-09-09 19:31, Tiezhu Yang wrote:
>>>
>>>> When testing the kernel live patching with "modprobe livepatch-sample",
>>>> there is a timeout over 15 seconds from "starting patching transition"
>>>> to "patching complete", dmesg shows "unreliable stack" for user tasks
>>>> in debug mode. When executing "rmmod livepatch-sample", there exists
>>>> the similar issue.

...

>> for this case, get_stack_info() does not return 0 due to in_task_stack()
>> is not true, then goto error, state->stack_info.type = STACK_TYPE_UNKNOWN
>> and state->error = true. In arch_stack_walk_reliable(), the loop will be
>> break and it returns -EINVAL, thus causing unreliable stack.
> The stop position of a complete stack backtrace on LoongArch should be
> the top of the task stack or until the address is_entry_func.
> Otherwise, it is not a complete stack backtrace, and thus I think it
> is an "unreliable stack".
> I'm curious about what the ORC info at this PC.

The unwind process has problem, I have found the root cause and am
working to fix the "unreliable stack" issue, it should and can find
the last frame, and then the user_mode() check is not necessary.

Thanks,
Tiezhu