From: Tero Kristo tero.kristo@linux.intel.com

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... Link: https://lkml.kernel.org/r/20230310100451.3948583-3-tero.kristo@linux.intel.c...

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 --- 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;

+ /* Do not start a new hwlatd thread if it is already running */ + if (per_cpu(hwlat_per_cpu_data, cpu).kthread) + return 0; + kthread = kthread_run_on_cpu(kthread_fn, NULL, cpu, "hwlatd/%u"); if (IS_ERR(kthread)) { pr_err(BANNER "could not start sampling thread\n");