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Subject[PATCH] rcu-tasks: Inspect stalled task's trc state in locked state
Date
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@quicinc.com>
---
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
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