linux-kernel - [PATCH] tracing: Quiet smp_processor_id() use in preemptable warning in hwlat

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Message-ID: <20210804141848.79edadc0@oasis.local.home>
Date:   Wed, 4 Aug 2021 14:18:48 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: [PATCH] tracing: Quiet smp_processor_id() use in preemptable
 warning in hwlat

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

The hardware latency detector (hwlat) has a mode that it runs one thread
across CPUs. The logic to move from the currently running CPU to the next
one in the list does a smp_processor_id() to find where it currently is.
Unfortunately, it's done with preemption enabled, and this triggers a
warning for using smp_processor_id() in a preempt enabled section.

As it is only using smp_processor_id() to get information on where it
currently is in order to simply move it to the next CPU, it doesn't really
care if it got moved in the mean time. It will simply balance out later if
such a case arises.

Switch smp_processor_id() to raw_smp_processor_id() to quiet that warning.

Fixes: 8fa826b7344d ("trace/hwlat: Implement the mode config option")
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace_hwlat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index a6c0cdaf4b87..14f46aae1981 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -327,7 +327,7 @@ static void move_to_next_cpu(void)

 	get_online_cpus();
 	cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
-	next_cpu = cpumask_next(smp_processor_id(), current_mask);
+	next_cpu = cpumask_next(raw_smp_processor_id(), current_mask);
 	put_online_cpus();

 	if (next_cpu >= nr_cpu_ids)
-- 
2.31.1