Re: [PATCH] lib/nmi_backtrace: print out the CPUs which fail to respond to NMI

[Andrew Morton]

On Fri, 22 May 2026 09:46:26 +0800 Feng Tang <feng.tang@xxxxxxxxxxxxxxxxx> wrote:

> > It's a nitpick, but
> > 
> > : 	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
> > : 	for (i = 0; i < 10 * 1000; i++) {
> > : 		if (cpumask_empty(to_cpumask(backtrace_mask)))
> > : 			break;
> > : 		mdelay(1);
> > : 		touch_softlockup_watchdog();
> > : 	}
> > : 
> > : 	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
> > : 		pr_warn("After 10 seconds, these CPUS still haven't responded to the NMI: %*pbl\n",
> > 
> > Here we're hard-coding "10" in two places and in a comment.  It would
> > be nicer to do
> > 
> > 	#define FOO_TIMEOUT 10
> > 
> > then use that throughout.
> > 
> > (bonus points for figuring out how to paste that "10" into the
> > pr_warn() control string rather than using %d!)
> 
> How about this followon patch?

Looks great.  But you missed the fun part!

--- a/lib/nmi_backtrace.c~lib-nmi_backtrace-print-out-the-cpus-which-fail-to-respond-to-nmi-fix-fix
+++ a/lib/nmi_backtrace.c
@@ -16,6 +16,7 @@
 #include <linux/cpumask.h>
 #include <linux/delay.h>
 #include <linux/kprobes.h>
+#include <linux/stringify.h>
 #include <linux/nmi.h>
 #include <linux/cpu.h>
 #include <linux/sched/debug.h>
@@ -79,8 +80,8 @@ void nmi_trigger_cpumask_backtrace(const
 	}
 
 	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
-		pr_warn("After %d seconds, these CPUS still haven't responded to the NMI: %*pbl\n",
-			NMI_BT_TIMEOUT_SEC, cpumask_pr_args(to_cpumask(backtrace_mask)));
+		pr_warn("After " __stringify(NMI_BT_TIMEOUT_SEC) " seconds, these CPUS still haven't responded to the NMI: %*pbl\n",
+			cpumask_pr_args(to_cpumask(backtrace_mask)));
 
 		nmi_backtrace_stall_check(to_cpumask(backtrace_mask));
 	}
_

It saved five bytes!