linux-kernel - Re: [PATCH 1/7] stop_machine: Introduce stop_machine

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Message-ID: <20260127144947.GKaXjQi8R9cE17WYKM@fat_crate.local>
Date: Tue, 27 Jan 2026 15:49:47 +0100
From: Borislav Petkov <bp@...en8.de>
To: kernel test robot <lkp@...el.com>
Cc: "Chang S. Bae" <chang.seok.bae@...el.com>, linux-kernel@...r.kernel.org,
	oe-kbuild-all@...ts.linux.dev, x86@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, dave.hansen@...ux.intel.com, peterz@...radead.org,
	david.kaplan@....com
Subject: Re: [PATCH 1/7] stop_machine: Introduce stop_machine_nmi()

On Mon, Jan 26, 2026 at 07:51:11PM +0800, kernel test robot wrote:
> Hi Chang,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on 24d479d26b25bce5faea3ddd9fa8f3a6c3129ea7]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Chang-S-Bae/stop_machine-Introduce-stop_machine_nmi/20260125-101013
> base:   24d479d26b25bce5faea3ddd9fa8f3a6c3129ea7
> patch link:    https://lore.kernel.org/r/20260125014224.249901-2-chang.seok.bae%40intel.com
> patch subject: [PATCH 1/7] stop_machine: Introduce stop_machine_nmi()
> config: x86_64-randconfig-r133-20260126 (https://download.01.org/0day-ci/archive/20260126/202601261901.Yj2kmvgI-lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260126/202601261901.Yj2kmvgI-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202601261901.Yj2kmvgI-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
> >> vmlinux.o: error: objtool: stop_machine_nmi_handler+0x23: call to {dynamic}() leaves .noinstr.text section

This one would be hard to fix because that's the

	err = msdata->fn(msdata->data);

function pointer which objtool can't see through.

So my suggestion would be to do:

struct nmi_multi_stop_data {
	cpu_stop_safe_fn_t           fn;

note the different function pointer type which we will hopefully catch during
review in the sense that only *safe* functions should be callable by the
NMI-specific stomp_machine.

Along with:

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 189b4b108d13..55a350048d4c 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -230,7 +230,9 @@ bool noinstr stop_machine_nmi_handler(void)
 	raw_cpu_write(stop_machine_nmi_ctrl.nmi_enabled, false);
 
 	msdata = raw_cpu_read(stop_machine_nmi_ctrl.msdata);
+	instrumentation_begin();
 	err = msdata->fn(msdata->data);
+	instrumentation_end();
 	raw_cpu_write(stop_machine_nmi_ctrl.err, err);
 	return true;
 }

ofc.

Unless someone has a better idea ofc...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette