linux-kernel - [PATCH v1 01/12] PM: sleep: Simplify dpm_suspended_list walk in dpm

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Date: Mon, 22 Jan 2024 12:22:38 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Ulf Hansson <ulf.hansson@...aro.org>, Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>
Subject: [PATCH v1 01/12] PM: sleep: Simplify dpm_suspended_list walk in dpm_resume()

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Notice that devices can be moved to dpm_prepared_list before running
their resume callbacks, in analogy with dpm_noirq_resume_devices() and
dpm_resume_early(), because doing so will not affect the final ordering
of that list.

Namely, if a device is the first dpm_suspended_list entry while
dpm_list_mtx is held, it has not been removed so far and it cannot be
removed until dpm_list_mtx is released, so moving it to dpm_prepared_list
at that point is valid.  If it is removed later, while its resume
callback is running, it will be deleted from dpm_prepared_list without
changing the ordering of the other devices in that list.

Accordingly, rearrange the while () loop in dpm_resume() to move
devices to dpm_prepared_list before running their resume callbacks and
implify the locking and device reference counting in it.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/base/power/main.c |   16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

Index: linux-pm/drivers/base/power/main.c
===================================================================
--- linux-pm.orig/drivers/base/power/main.c
+++ linux-pm/drivers/base/power/main.c
@@ -1017,25 +1017,19 @@ void dpm_resume(pm_message_t state)

 	while (!list_empty(&dpm_suspended_list)) {
 		dev = to_device(dpm_suspended_list.next);
-
-		get_device(dev);
+		list_move_tail(&dev->power.entry, &dpm_prepared_list);

 		if (!dev->power.async_in_progress) {
+			get_device(dev);
+
 			mutex_unlock(&dpm_list_mtx);

 			device_resume(dev, state, false);

+			put_device(dev);
+
 			mutex_lock(&dpm_list_mtx);
 		}
-
-		if (!list_empty(&dev->power.entry))
-			list_move_tail(&dev->power.entry, &dpm_prepared_list);
-
-		mutex_unlock(&dpm_list_mtx);
-
-		put_device(dev);
-
-		mutex_lock(&dpm_list_mtx);
 	}
 	mutex_unlock(&dpm_list_mtx);
 	async_synchronize_full();