tracing/hwlat: Replace sched_setaffinity with set_cpus_allowed_ptr

There is a problem with the behavior of hwlat in a container,
resulting in incorrect output. A warning message is generated:
"cpumask changed while in round-robin mode, switching to mode none",
and the tracing_cpumask is ignored. This issue arises because
the kernel thread, hwlatd, is not a part of the container, and
the function sched_setaffinity is unable to locate it using its PID.
Additionally, the task_struct of hwlatd is already known.
Ultimately, the function set_cpus_allowed_ptr achieves
the same outcome as sched_setaffinity, but employs task_struct
instead of PID.

Test case:

  # cd /sys/kernel/tracing
  # echo 0 > tracing_on
  # echo round-robin > hwlat_detector/mode
  # echo hwlat > current_tracer
  # unshare --fork --pid bash -c 'echo 1 > tracing_on'
  # dmesg -c

Actual behavior:

[573502.809060] hwlat_detector: cpumask changed while in round-robin mode, switching to mode none

Link: https://lore.kernel.org/linux-trace-kernel/20230316144535.1004952-1-costa.shul@redhat.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 0330f7aa8ee63 ("tracing: Have hwlat trace migrate across tracing_cpumask CPUs")
Signed-off-by: Costa Shulyupin <costa.shul@redhat.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 c4945f8adc119c76dca5ec359f523bad69773e94..2f37a6e68aa9f851f19b968eeafdb1034d3efae2 100644 (file)
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -339,7 +339,7 @@ static void move_to_next_cpu(void)
        cpumask_clear(current_mask);
        cpumask_set_cpu(next_cpu, current_mask);
 
-       sched_setaffinity(0, current_mask);
+       set_cpus_allowed_ptr(current, current_mask);
        return;
 
  change_mode:
@@ -446,7 +446,7 @@ static int start_single_kthread(struct trace_array *tr)
 
        }
 
-       sched_setaffinity(kthread->pid, current_mask);
+       set_cpus_allowed_ptr(kthread, current_mask);
 
        kdata->kthread = kthread;
        wake_up_process(kthread);