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tracing/hwlat: Replace sched_setaffinity with set_cpus_allowed_ptr

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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>
This commit is contained in:
Costa Shulyupin 2023-03-16 16:45:35 +02:00 committed by Steven Rostedt (Google)
parent a98151ad53
commit 71c7a30442
1 changed files with 2 additions and 2 deletions
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4
kernel/trace/trace_hwlat.c
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@ -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);