linux-kernel - [PATCH 4/6] driver core: Do not resume suppliers under device_links_write

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Message-ID: <6978367.mo1Yi9LooT@aspire.rjw.lan>
Date:   Thu, 24 Jan 2019 12:19:35 +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>
Subject: [PATCH 4/6] driver core: Do not resume suppliers under device_links_write_lock()

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

It is incorrect to call pm_runtime_get_sync() under
device_links_write_lock(), because it may end up trying to take
device_links_read_lock() while resuming the target device and that
will deadlock in the non-SRCU case, so avoid that by resuming the
supplier device in device_link_add() before calling
device_links_write_lock().

Fixes: 21d5c57b3726 ("PM / runtime: Use device links")
Fixes: baa8809f6097 ("PM / runtime: Optimize the use of device links")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/base/core.c |   20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -202,12 +202,21 @@ struct device_link *device_link_add(stru
 				    struct device *supplier, u32 flags)
 {
 	struct device_link *link;
+	bool rpm_put_supplier = false;
 
 	if (!consumer || !supplier ||
 	    (flags & DL_FLAG_STATELESS &&
 	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER | DL_FLAG_AUTOREMOVE_SUPPLIER)))
 		return NULL;
 
+	if (flags & DL_FLAG_PM_RUNTIME && flags & DL_FLAG_RPM_ACTIVE) {
+		if (pm_runtime_get_sync(supplier) < 0) {
+			pm_runtime_put_noidle(supplier);
+			return NULL;
+		}
+		rpm_put_supplier = true;
+	}
+
 	device_links_write_lock();
 	device_pm_lock();
 
@@ -251,13 +260,8 @@ struct device_link *device_link_add(stru
 
 	if (flags & DL_FLAG_PM_RUNTIME) {
 		if (flags & DL_FLAG_RPM_ACTIVE) {
-			if (pm_runtime_get_sync(supplier) < 0) {
-				pm_runtime_put_noidle(supplier);
-				kfree(link);
-				link = NULL;
-				goto out;
-			}
 			link->rpm_active = true;
+			rpm_put_supplier = false;
 		}
 		pm_runtime_new_link(consumer);
 		/*
@@ -329,6 +333,10 @@ struct device_link *device_link_add(stru
  out:
 	device_pm_unlock();
 	device_links_write_unlock();
+
+	if (rpm_put_supplier)
+		pm_runtime_put(supplier);
+
 	return link;
 }
 EXPORT_SYMBOL_GPL(device_link_add);