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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Linux PM <linux-pm@vger.kernel.org>
Cc:     "elaine.zhang" <zhangqing@rock-chips.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>
Subject: [PATCH v2 1/2] Revert "PM: runtime: Update device status before letting suppliers suspend"
Date:   Fri, 19 Mar 2021 15:47:25 +0100
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In-Reply-To: <4641414.31r3eYUQgx@kreacher>
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From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

Revert commit 44cc89f76464 ("PM: runtime: Update device status
before letting suppliers suspend") that introduced a race condition
into __rpm_callback() which allowed a concurrent rpm_resume() to
run and resume the device prematurely after its status had been
changed to RPM_SUSPENDED by __rpm_callback().

Fixes: 44cc89f76464 ("PM: runtime: Update device status before letting suppliers suspend")
Link: https://lore.kernel.org/linux-pm/24dfb6fc-5d54-6ee2-9195-26428b7ecf8a@intel.com/
Reported by: Adrian Hunter <adrian.hunter@intel.com>
Cc: 4.10+ <stable@vger.kernel.org> # 4.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
---

v1 -> v2: Added the R-by tag from Ulf.

---
 drivers/base/power/runtime.c | 62 +++++++++++++++---------------------
 1 file changed, 25 insertions(+), 37 deletions(-)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 18b82427d0cb..a46a7e30881b 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -325,22 +325,22 @@ static void rpm_put_suppliers(struct device *dev)
 static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
 	__releases(&dev->power.lock) __acquires(&dev->power.lock)
 {
-	bool use_links = dev->power.links_count > 0;
-	bool get = false;
 	int retval, idx;
-	bool put;
+	bool use_links = dev->power.links_count > 0;
 
 	if (dev->power.irq_safe) {
 		spin_unlock(&dev->power.lock);
-	} else if (!use_links) {
-		spin_unlock_irq(&dev->power.lock);
 	} else {
-		get = dev->power.runtime_status == RPM_RESUMING;
-
 		spin_unlock_irq(&dev->power.lock);
 
-		/* Resume suppliers if necessary. */
-		if (get) {
+		/*
+		 * Resume suppliers if necessary.
+		 *
+		 * The device's runtime PM status cannot change until this
+		 * routine returns, so it is safe to read the status outside of
+		 * the lock.
+		 */
+		if (use_links && dev->power.runtime_status == RPM_RESUMING) {
 			idx = device_links_read_lock();
 
 			retval = rpm_get_suppliers(dev);
@@ -355,36 +355,24 @@ static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
 
 	if (dev->power.irq_safe) {
 		spin_lock(&dev->power.lock);
-		return retval;
-	}
-
-	spin_lock_irq(&dev->power.lock);
-
-	if (!use_links)
-		return retval;
-
-	/*
-	 * If the device is suspending and the callback has returned success,
-	 * drop the usage counters of the suppliers that have been reference
-	 * counted on its resume.
-	 *
-	 * Do that if the resume fails too.
-	 */
-	put = dev->power.runtime_status == RPM_SUSPENDING && !retval;
-	if (put)
-		__update_runtime_status(dev, RPM_SUSPENDED);
-	else
-		put = get && retval;
-
-	if (put) {
-		spin_unlock_irq(&dev->power.lock);
-
-		idx = device_links_read_lock();
+	} else {
+		/*
+		 * If the device is suspending and the callback has returned
+		 * success, drop the usage counters of the suppliers that have
+		 * been reference counted on its resume.
+		 *
+		 * Do that if resume fails too.
+		 */
+		if (use_links
+		    && ((dev->power.runtime_status == RPM_SUSPENDING && !retval)
+		    || (dev->power.runtime_status == RPM_RESUMING && retval))) {
+			idx = device_links_read_lock();
 
-fail:
-		rpm_put_suppliers(dev);
+ fail:
+			rpm_put_suppliers(dev);
 
-		device_links_read_unlock(idx);
+			device_links_read_unlock(idx);
+		}
 
 		spin_lock_irq(&dev->power.lock);
 	}
-- 
2.26.2