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

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Message-ID: <alpine.LSU.2.21.2509111541590.29971@pobox.suse.cz>
Date: Thu, 11 Sep 2025 15:44:53 +0200 (CEST)
From: Miroslav Benes <mbenes@...e.cz>
To: Tiezhu Yang <yangtiezhu@...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()

Hi,

On Tue, 9 Sep 2025, 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.
> 
> Like x86, arch_stack_walk_reliable() should return 0 for user tasks.
> It is necessary to set regs->csr_prmd as task->thread.csr_prmd first,
> then use user_mode() to check whether the task is in userspace.

it is a nice optimization for sure, but "unreliable stack" messages point 
to a fact that the unwinding of these tasks is probably suboptimal and 
could be improved, no?

It would also be nice to include these messages (not for all tasks) to the 
commit message.

Regards
Miroslav