linux-kernel - [PATCH 1/2] PM-runtime: Fix __pm_runtime_set

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Date:   Tue, 12 Feb 2019 13:04:12 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Lukas Wunner <lukas@...ner.de>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Lucas Stach <l.stach@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: [PATCH 1/2] PM-runtime: Fix __pm_runtime_set_status() race with runtime resume

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

Commit 4080ab083000 ("PM-runtime: Take suppliers into account in
__pm_runtime_set_status()") introduced a race condition that may
trigger if __pm_runtime_set_status() is used incorrectly (that is,
if it is called when PM-runtime is enabled for the target device
and working).

In that case, if the original PM-runtime status of the device is
RPM_SUSPENDED, a runtime resume of the device may occur after
__pm_runtime_set_status() has dropped its power.lock spinlock
and before deactivating its suppliers, so the suppliers may be
deactivated while the device is PM-runtime-active which may lead
to functional issues.

To avoid that, modify __pm_runtime_set_status() to check whether
or not PM-runtime is enabled for the device before activating its
suppliers (if the new status is RPM_ACTIVE) and either return an
error if that's the case or increment the device's disable_depth
counter to prevent PM-runtime from being enabled for it while
the remaining part of the function is running (disable_depth is
then decremented on the way out).

Fixes: 4080ab083000 ("PM-runtime: Take suppliers into account in __pm_runtime_set_status()")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/base/power/runtime.c |   24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -1129,6 +1129,22 @@ int __pm_runtime_set_status(struct devic
 	if (status != RPM_ACTIVE && status != RPM_SUSPENDED)
 		return -EINVAL;

+	spin_lock_irq(&dev->power.lock);
+
+	/*
+	 * Prevent PM-runtime from being enabled for the device or return an
+	 * error if it is enabled already and working.
+	 */
+	if (dev->power.runtime_error || dev->power.disable_depth)
+		dev->power.disable_depth++;
+	else
+		error = -EAGAIN;
+
+	spin_unlock_irq(&dev->power.lock);
+
+	if (error)
+		return error;
+
 	/*
 	 * If the new status is RPM_ACTIVE, the suppliers can be activated
 	 * upfront regardless of the current status, because next time
@@ -1147,12 +1163,6 @@ int __pm_runtime_set_status(struct devic

 	spin_lock_irq(&dev->power.lock);

-	if (!dev->power.runtime_error && !dev->power.disable_depth) {
-		status = dev->power.runtime_status;
-		error = -EAGAIN;
-		goto out;
-	}
-
 	if (dev->power.runtime_status == status || !parent)
 		goto out_set;

@@ -1205,6 +1215,8 @@ int __pm_runtime_set_status(struct devic
 		device_links_read_unlock(idx);
 	}

+	pm_runtime_enable(dev);
+
 	return error;
 }
 EXPORT_SYMBOL_GPL(__pm_runtime_set_status);