linux-kernel - [PATCH 1/2] drivers: base: power: main.c: Use built-in RCU list checking

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Date:   Wed,  4 Mar 2020 01:11:30 +0530
From:   madhuparnabhowmik10@...il.com
To:     rjw@...ysocki.net, pavel@....cz, len.brown@...el.com,
        gregkh@...uxfoundation.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        joel@...lfernandes.org, frextrite@...il.com,
        linux-kernel-mentees@...ts.linuxfoundation.org, paulmck@...nel.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Subject: [PATCH 1/2] drivers: base: power: main.c: Use built-in RCU list checking

From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>

This patch passes the cond argument to list_for_each_entry_rcu()
to fix the following false-positive lockdep warnings:
(with CONFIG_PROVE_RCU_LIST = y)

[  330.302784] =============================
[  330.302789] WARNING: suspicious RCU usage
[  330.302796] 5.6.0-rc1+ #5 Not tainted
[  330.302801] -----------------------------
[  330.302808] drivers/base/power/main.c:326 RCU-list traversed in non-reader section!!

[  330.303303] =============================
[  330.303307] WARNING: suspicious RCU usage
[  330.303311] 5.6.0-rc1+ #5 Not tainted
[  330.303315] -----------------------------
[  330.303319] drivers/base/power/main.c:1698 RCU-list traversed in non-reader section!!

[  331.934969] =============================
[  331.934971] WARNING: suspicious RCU usage
[  331.934973] 5.6.0-rc1+ #5 Not tainted
[  331.934975] -----------------------------
[  331.934977] drivers/base/power/main.c:1238 RCU-list traversed in non-reader section!!

[  332.467772] WARNING: suspicious RCU usage
[  332.467775] 5.6.0-rc1+ #5 Not tainted
[  332.467775] -----------------------------
[  332.467778] drivers/base/power/main.c:269 RCU-list traversed in non-reader section!!

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
---
 drivers/base/power/main.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 0e99a760aebd..6d1dee7051eb 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -40,6 +40,10 @@
 
 typedef int (*pm_callback_t)(struct device *);
 
+#define list_for_each_entry_rcu_locked(pos, head, member) \
+	list_for_each_entry_rcu(pos, head, member, \
+			device_links_read_lock_held())
+
 /*
  * The entries in the dpm_list list are in a depth first order, simply
  * because children are guaranteed to be discovered after parents, and
@@ -266,7 +270,7 @@ static void dpm_wait_for_suppliers(struct device *dev, bool async)
 	 * callbacks freeing the link objects for the links in the list we're
 	 * walking.
 	 */
-	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
+	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
 		if (READ_ONCE(link->status) != DL_STATE_DORMANT)
 			dpm_wait(link->supplier, async);
 
@@ -323,7 +327,7 @@ static void dpm_wait_for_consumers(struct device *dev, bool async)
 	 * continue instead of trying to continue in parallel with its
 	 * unregistration).
 	 */
-	list_for_each_entry_rcu(link, &dev->links.consumers, s_node)
+	list_for_each_entry_rcu_locked(link, &dev->links.consumers, s_node)
 		if (READ_ONCE(link->status) != DL_STATE_DORMANT)
 			dpm_wait(link->consumer, async);
 
@@ -1235,7 +1239,7 @@ static void dpm_superior_set_must_resume(struct device *dev)
 
 	idx = device_links_read_lock();
 
-	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
+	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
 		link->supplier->power.must_resume = true;
 
 	device_links_read_unlock(idx);
@@ -1695,7 +1699,7 @@ static void dpm_clear_superiors_direct_complete(struct device *dev)
 
 	idx = device_links_read_lock();
 
-	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node) {
+	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node) {
 		spin_lock_irq(&link->supplier->power.lock);
 		link->supplier->power.direct_complete = false;
 		spin_unlock_irq(&link->supplier->power.lock);
-- 
2.17.1