[PATCH] trace/hwlat: Do not restart per-cpu threads if they are already running
STALE1302d
LANDED
From: Tero Kristo <hidden>
Date: 2023-03-02 11:38:37
Also in:
lkml
Subsystem:
the rest, tracing, tracing os noise / latency tracers · Maintainers:
Linus Torvalds, Steven Rostedt, Masami Hiramatsu
Landed in mainline as 4c42f5f0d1dd on 2023-03-19.
Check if the hwlatd thread for the cpu is already running, before starting a new one. This avoids running multiple instances of the same CPU thread on the system. Also, do not wipe the contents of the per-cpu kthread data when starting the tracer, as this can completely forget about already running instances and start new additional per-cpu threads. Fixes issues where fiddling with either the mode of the hwlat tracer or doing cpu-hotplugs messes up the internal book-keeping resulting in stale hwlatd threads. Signed-off-by: Tero Kristo <redacted> --- kernel/trace/trace_hwlat.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index d440ddd5fd8b..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");
@@ -584,9 +588,6 @@ static int start_per_cpu_kthreads(struct trace_array *tr) */ cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask); - for_each_online_cpu(cpu) - per_cpu(hwlat_per_cpu_data, cpu).kthread = NULL; - for_each_cpu(cpu, current_mask) { retval = start_cpu_kthread(cpu); if (retval)
--
2.25.1