linux-kernel - [PATCH v1 2/5] PM: sleep: Remove unnecessary mutex lock when waiting on parent

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Message-Id: <20241114220921.2529905-3-saravanak@google.com>
Date: Thu, 14 Nov 2024 14:09:16 -0800
From: Saravana Kannan <saravanak@...gle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>
Cc: Saravana Kannan <saravanak@...gle.com>, Geert Uytterhoeven <geert@...ux-m68k.org>, 
	Marek Vasut <marex@...x.de>, Bird@...gle.com, Tim <Tim.Bird@...y.com>, 
	kernel-team@...roid.com, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 2/5] PM: sleep: Remove unnecessary mutex lock when waiting
 on parent

Locking is not needed to do get_device(dev->parent). We either get a NULL
(if the parent was cleared) or the actual parent. Also, when a device is
deleted (device_del()) and removed from the dpm_list, its completion
variable is also complete_all()-ed. So, we don't have to worry about
waiting indefinitely on a deleted parent device.

Signed-off-by: Saravana Kannan <saravanak@...gle.com>
---
 drivers/base/power/main.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 86e51b9fefab..9b9b6088e56a 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -284,18 +284,9 @@ static bool dpm_wait_for_superior(struct device *dev, bool async)
 	 * counting the parent once more unless the device has been deleted
 	 * already (in which case return right away).
 	 */
-	mutex_lock(&dpm_list_mtx);
-
-	if (!device_pm_initialized(dev)) {
-		mutex_unlock(&dpm_list_mtx);
-		return false;
-	}
-
 	parent = get_device(dev->parent);
-
-	mutex_unlock(&dpm_list_mtx);
-
-	dpm_wait(parent, async);
+	if (device_pm_initialized(dev))
+		dpm_wait(parent, async);
 	put_device(parent);
 
 	dpm_wait_for_suppliers(dev, async);
-- 
2.47.0.338.g60cca15819-goog