From: Tero Kristo <tero.kristo@linux.intel.com>
Date: Fri, 10 Mar 2023 12:04:51 +0200
Subject: trace/hwlat: Do not start per-cpu thread if it is already running
Git-commit: 08697bca9bbba15f2058fdbd9f970bd5f6a8a2e8
Patch-mainline: v6.3-rc3
References: git-fixes
The hwlatd tracer will end up starting multiple per-cpu threads with
the following script:
#!/bin/sh
cd /sys/kernel/debug/tracing
echo 0 > tracing_on
echo hwlat > current_tracer
echo per-cpu > hwlat_detector/mode
echo 100000 > hwlat_detector/width
echo 200000 > hwlat_detector/window
echo 1 > tracing_on
To fix the issue, check if the hwlatd thread for the cpu is already
running, before starting a new one. Along with the previous patch, this
avoids running multiple instances of the same CPU thread on the system.
Link: https://lore.kernel.org/all/20230302113654.2984709-1-tero.kristo@linux.intel.com/
Link: https://lkml.kernel.org/r/20230310100451.3948583-3-tero.kristo@linux.intel.com
Cc: stable@vger.kernel.org
Fixes: f46b16520a087 ("trace/hwlat: Implement the per-cpu mode")
Signed-off-by: Tero Kristo <tero.kristo@linux.intel.com>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Petr Pavlu <petr.pavlu@suse.com>
---
kernel/trace/trace_hwlat.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index edc26dc22c3f..c4945f8adc11 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -492,6 +492,10 @@ static int start_cpu_kthread(unsigned int cpu)
struct task_struct *kthread;
char comm[24];
+ /* Do not start a new hwlatd thread if it is already running */
+ if (per_cpu(hwlat_per_cpu_data, cpu).kthread)
+ return 0;
+
snprintf(comm, 24, "hwlatd/%d", cpu);
kthread = kthread_create_on_cpu(kthread_fn, NULL, cpu, comm);