linux内核休眠、唤醒流程分析之挂起：Call Notifiers、Freeze任务（三）

最新推荐文章于 2025-05-05 19:59:15 发布

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本文深入探讨Linux内核的休眠挂起过程，详细解析了pm_suspend入口函数及其调用的enter_state函数。在挂起过程中，通过特定机制实现了流程图中的步骤1和步骤2，即调用call notifiers执行过程1，然后通过freeze任务完成对APP和内核线程的冻结，确保系统的稳定挂起。

在这里插入图片描述

入口函数为pm_suspend

// kernel\power\suspend.c

/**
 * pm_suspend - Externally visible function for suspending the system.
 * @state: System sleep state to enter.
 *
 * Check if the value of @state represents one of the supported states,
 * execute enter_state() and update system suspend statistics.
 */
int pm_suspend(suspend_state_t state)
{
	int error;

	if (state <= PM_SUSPEND_ON || state >= PM_SUSPEND_MAX)
		return -EINVAL;

	pr_info("suspend entry (%s)\n", mem_sleep_labels[state]);
	error = enter_state(state);
	if (error) {
		suspend_stats.fail++;
		dpm_save_failed_errno(error);
	} else {
		suspend_stats.success++;
	}
	pr_info("suspend exit\n");
	return error;
}
EXPORT_SYMBOL(pm_suspend);

这里会执行enter_state函数。

/**
 * enter_state - Do common work needed to enter system sleep state.
 * @state: System sleep state to enter.
 *
 * Make sure that no one else is trying to put the system into a sleep state.
 * Fail if that's not the case.  Otherwise, prepare for system suspend, make the
 * system enter the given sleep state and clean up after wakeup.
 */
static int enter_state(suspend_state_t state)
{
	int error;

	trace_suspend_resume(TPS("suspend_enter"), state, true);
	if (state == PM_SUSPEND_TO_IDLE) {
#ifdef CONFIG_PM_DEBUG
		if (pm_test_level != TEST_NONE && pm_test_level <= TEST_CPUS) {
			pr_warn("Unsupported test mode for suspend to idle, please choose none/freezer/devices/platform.\n");
			return -EAGAIN;
		}
#endif
	} else if (!valid_state(state)) {
		return -EINVAL;
	}
	if (!mutex_trylock(&system_transition_mutex))
		return -EBUSY;

	if (state == PM_SUSPEND_TO_IDLE)
		s2idle_begin();

	if (sync_on_suspend_enabled) {
		trace_suspend_resume(TPS("sync_filesystems"), 0, true);
		ksys_sync_helper();
		trace_suspend_resume(TPS("sync_filesystems"), 0, false);
	}

	pm_pr_dbg("Preparing system for sleep (%s)\n", mem_sleep_labels[state]);
	pm_suspend_clear_flags();
	error = suspend_prepare(state);
	if (error)
		goto Unlock;

	if (suspend_test(TEST_FREEZER))
		goto Finish;

	trace_suspend_resume(TPS("suspend_enter"), state, false);
	pm_pr_dbg("Suspending system (%s)\n", mem_sleep_labels[state]);
	pm_restrict_gfp_mask();
	error = suspend_devices_and_enter(state);
	pm_restore_gfp_mask();

 Finish:
	events_check_enabled = false;
	pm_pr_dbg("Finishing wakeup.\n");
	suspend_finish();
 Unlock:
	mutex_unlock(&system_transition_mutex);
	return error;
}

首先是调用

// kernel\power\suspend.c

/**
 * suspend_prepare - Prepare for entering system sleep state.
 *
 * Common code run for every system sleep state that can be entered (except for
 * hibernation).  Run suspend notifiers, allocate the "suspend" console and
 * freeze processes.
 */
static int suspend_prepare(suspend_state_t state)
{
	int error, nr_calls = 0;

	if (!sleep_state_supported(state))
		return -EPERM;

	pm_prepare_console();

	error = __pm_notifier_call_chain(PM_SUSPEND_PREPARE, -1, &nr_calls);
	if (error) {
		nr_calls--;
		goto Finish;
	}

	trace_suspend_resume(TPS("freeze_processes"), 0, true);
	error = suspend_freeze_processes();
	trace_suspend_resume(TPS("freeze_processes"), 0, false);
	if (!error)
		return 0;

	suspend_stats.failed_freeze++;
	dpm_save_failed_step(SUSPEND_FREEZE);
 Finish:
	__pm_notifier_call_chain(PM_POST_SUSPEND, nr_calls, NULL);
	pm_restore_console();
	return error;
}

其中通过

error = __pm_notifier_call_chain(PM_SUSPEND_PREPARE, -1, &nr_calls);

实现流程图中的过程1.
通过

error = suspend_freeze_processes();

实现流程图中的过程2，冻结APP和内核线程。