[Linux-kernel-mentees] [PATCH] ipmi: Fix RCU list lockdep debugging warnings

[Amol Grover <frextrite@gmail.com>]

It is completely safe to traverse ipmi_interfaces and
intf->users under SRCU read lock using list_for_each_entry_rcu().
Tell lockdep about it as well else it will show false-positive
warnings as the one below.

Fixes the following false-positive warning and others that may follow.

[   29.772408] =============================
[   29.776863] WARNING: suspicious RCU usage
[   29.780915] 5.6.0-rc3-00001-g907305ae6618-dirty #1755 Not tainted
[   29.787046] -----------------------------
[   29.791100] drivers/char/ipmi/ipmi_msghandler.c:744 RCU-list traversed in
non-reader section!!

Reported-by: John Garry <john.garry@huawei.com>
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Amol Grover <frextrite@gmail.com>
---
 drivers/char/ipmi/ipmi_msghandler.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index cad9563f8f48..d202022c69de 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -741,7 +741,8 @@ int ipmi_smi_watcher_register(struct ipmi_smi_watcher *watcher)
 	list_add(&watcher->link, &smi_watchers);
 
 	index = srcu_read_lock(&ipmi_interfaces_srcu);
-	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
+	list_for_each_entry_rcu(intf, &ipmi_interfaces, link,
+				srcu_read_lock_held(&ipmi_interfaces_srcu)) {
 		int intf_num = READ_ONCE(intf->intf_num);
 
 		if (intf_num == -1)
@@ -1188,7 +1189,8 @@ int ipmi_create_user(unsigned int          if_num,
 		return -ENOMEM;
 
 	index = srcu_read_lock(&ipmi_interfaces_srcu);
-	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
+	list_for_each_entry_rcu(intf, &ipmi_interfaces, link,
+				srcu_read_lock_held(&ipmi_interfaces_srcu)) {
 		if (intf->intf_num == if_num)
 			goto found;
 	}
@@ -1241,7 +1243,8 @@ int ipmi_get_smi_info(int if_num, struct ipmi_smi_info *data)
 	struct ipmi_smi *intf;
 
 	index = srcu_read_lock(&ipmi_interfaces_srcu);
-	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
+	list_for_each_entry_rcu(intf, &ipmi_interfaces, link,
+				srcu_read_lock_held(&ipmi_interfaces_srcu)) {
 		if (intf->intf_num == if_num)
 			goto found;
 	}
@@ -4098,7 +4101,8 @@ static int handle_read_event_rsp(struct ipmi_smi *intf,
 	 * getting events.
 	 */
 	index = srcu_read_lock(&intf->users_srcu);
-	list_for_each_entry_rcu(user, &intf->users, link) {
+	list_for_each_entry_rcu(user, &intf->users, link,
+				srcu_read_lock_held(&intf->users_srcu)) {
 		if (!user->gets_events)
 			continue;
 
@@ -4453,7 +4457,8 @@ static void handle_new_recv_msgs(struct ipmi_smi *intf)
 		int index;
 
 		index = srcu_read_lock(&intf->users_srcu);
-		list_for_each_entry_rcu(user, &intf->users, link) {
+		list_for_each_entry_rcu(user, &intf->users, link,
+					srcu_read_lock_held(&intf->users_srcu)) {
 			if (user->handler->ipmi_watchdog_pretimeout)
 				user->handler->ipmi_watchdog_pretimeout(
 					user->handler_data);
@@ -4746,7 +4751,8 @@ static void ipmi_timeout(struct timer_list *unused)
 		return;
 
 	index = srcu_read_lock(&ipmi_interfaces_srcu);
-	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
+	list_for_each_entry_rcu(intf, &ipmi_interfaces, link,
+				srcu_read_lock_held(&ipmi_interfaces_srcu)) {
 		if (atomic_read(&intf->event_waiters)) {
 			intf->ticks_to_req_ev--;
 			if (intf->ticks_to_req_ev == 0) {
-- 
2.25.0

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