On Tue, Nov 09, 2021 at 04:52:14PM +0530, Neeraj Upadhyay wrote:
> On RCU tasks trace stall, inspect the RCU-tasks-trace specific
> states of stalled task in locked down state, using try_invoke_
> on_locked_down_task(), to get reliable trc state of a non-running
> stalled task.
>
> Signed-off-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
Queued for further review and testing, thank you!
Along those lines, what did you do to test this? I would like to
add that to the commit message. (The usual approach is to use the
rcutorture.stall_cpu module parameter, in case I have not yet passed
that along.)
Thanx, Paul
> ---
> kernel/rcu/tasks.h | 43 ++++++++++++++++++++++++++++++++++---------
> 1 file changed, 34 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index e4a32db9f712..4e49b847971b 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -1073,25 +1073,50 @@ static void rcu_tasks_trace_postscan(struct list_head *hop)
> // Any tasks that exit after this point will set ->trc_reader_checked.
> }
>
> +/* Communicate task state back to the RCU tasks trace stall warning request. */
> +struct trc_stall_chk_rdr {
> + int nesting;
> + int ipi_to_cpu;
> + u8 needqs;
> +};
> +
> +static bool trc_check_slow_task(struct task_struct *t, void *arg)
> +{
> + struct trc_stall_chk_rdr *trc_rdrp = arg;
> +
> + if (task_curr(t))
> + return false; // It is running, so decline to inspect it.
> + trc_rdrp->nesting = READ_ONCE(t->trc_reader_nesting);
> + trc_rdrp->ipi_to_cpu = READ_ONCE(t->trc_ipi_to_cpu);
> + trc_rdrp->needqs = READ_ONCE(t->trc_reader_special.b.need_qs);
> + return true;
> +}
> +
> /* Show the state of a task stalling the current RCU tasks trace GP. */
> static void show_stalled_task_trace(struct task_struct *t, bool *firstreport)
> {
> int cpu;
> + struct trc_stall_chk_rdr trc_rdr;
> + bool is_idle_tsk = is_idle_task(t);
>
> if (*firstreport) {
> pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n");
> *firstreport = false;
> }
> - // FIXME: This should attempt to use try_invoke_on_nonrunning_task().
> cpu = task_cpu(t);
> - pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n",
> - t->pid,
> - ".I"[READ_ONCE(t->trc_ipi_to_cpu) >= 0],
> - ".i"[is_idle_task(t)],
> - ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)],
> - READ_ONCE(t->trc_reader_nesting),
> - " N"[!!READ_ONCE(t->trc_reader_special.b.need_qs)],
> - cpu);
> + if (!try_invoke_on_locked_down_task(t, trc_check_slow_task, &trc_rdr))
> + pr_alert("P%d: %c\n",
> + t->pid,
> + ".i"[is_idle_tsk]);
> + else
> + pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n",
> + t->pid,
> + ".I"[trc_rdr.ipi_to_cpu >= 0],
> + ".i"[is_idle_tsk],
> + ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)],
> + trc_rdr.nesting,
> + " N"[!!trc_rdr.needqs],
> + cpu);
> sched_show_task(t);
> }
>
> --
> 2.17.1
>
