rcu-tasks: Add stall warnings for RCU Tasks Trace (4593e772) · Commits · 戴 / test

kernel/rcu/tasks.h

+66 −4

Original line number	Diff line number	Diff line
		@@ -798,9 +798,41 @@ static void rcu_tasks_trace_postscan(void)
		// Any tasks that exit after this point will set ->trc_reader_checked.
		}

		/* 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;

		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)],
		t->trc_reader_nesting,
		" N"[!!t->trc_reader_need_end],
		cpu);
		sched_show_task(t);
		}

		/* List stalled IPIs for RCU tasks trace. */
		static void show_stalled_ipi_trace(void)
		{
		int cpu;

		for_each_possible_cpu(cpu)
		if (per_cpu(trc_ipi_to_cpu, cpu))
		pr_alert("\tIPI outstanding to CPU %d\n", cpu);
		}

		/* Do one scan of the holdout list. */
		static void check_all_holdout_tasks_trace(struct list_head *hop,
		bool ndrpt, bool *frptp)
		bool needreport, bool *firstreport)
		{
		struct task_struct g, t;

		@@ -813,21 +845,51 @@ static void check_all_holdout_tasks_trace(struct list_head *hop,
		// If check succeeded, remove this task from the list.
		if (READ_ONCE(t->trc_reader_checked))
		trc_del_holdout(t);
		else if (needreport)
		show_stalled_task_trace(t, firstreport);
		}
		if (needreport) {
		if (firstreport)
		pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n");
		show_stalled_ipi_trace();
		}
		}

		/* Wait for grace period to complete and provide ordering. */
		static void rcu_tasks_trace_postgp(void)
		{
		bool firstreport;
		struct task_struct g, t;
		LIST_HEAD(holdouts);
		long ret;

		// Remove the safety count.
		smp_mb__before_atomic(); // Order vs. earlier atomics
		atomic_dec(&trc_n_readers_need_end);
		smp_mb__after_atomic(); // Order vs. later atomics

		// Wait for readers.
		wait_event_idle_exclusive(trc_wait,
		atomic_read(&trc_n_readers_need_end) == 0);

		for (;;) {
		ret = wait_event_idle_exclusive_timeout(
		trc_wait,
		atomic_read(&trc_n_readers_need_end) == 0,
		READ_ONCE(rcu_task_stall_timeout));
		if (ret)
		break; // Count reached zero.
		for_each_process_thread(g, t)
		if (READ_ONCE(t->trc_reader_need_end))
		trc_add_holdout(t, &holdouts);
		firstreport = true;
		list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list)
		if (READ_ONCE(t->trc_reader_need_end)) {
		show_stalled_task_trace(t, &firstreport);
		trc_del_holdout(t);
		}
		if (firstreport)
		pr_err("INFO: rcu_tasks_trace detected stalls? (Counter/taskslist mismatch?)\n");
		show_stalled_ipi_trace();
		pr_err("\t%d holdouts\n", atomic_read(&trc_n_readers_need_end));
		}
		smp_mb(); // Caller's code must be ordered after wakeup.
		}

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