The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 08697bca9bbba15f2058fdbd9f970bd5f6a8a2e8 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '167931291995243@kroah.com' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

08697bca9bbb ("trace/hwlat: Do not start per-cpu thread if it is already running") ff78f6679d2e ("trace/hwlat: make use of the helper function kthread_run_on_cpu()")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 08697bca9bbba15f2058fdbd9f970bd5f6a8a2e8 Mon Sep 17 00:00:00 2001 From: Tero Kristo tero.kristo@linux.intel.com Date: Fri, 10 Mar 2023 12:04:51 +0200 Subject: [PATCH] trace/hwlat: Do not start per-cpu thread if it is already running

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

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");