linux-kernel - [PATCH v3] drivers: char: ipmi: ipmi_msghandler: Pass lockdep expression to RCU lists

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Message-Id: <20200117132521.31020-1-frextrite@gmail.com>
Date:   Fri, 17 Jan 2020 18:55:22 +0530
From:   Amol Grover <frextrite@...il.com>
To:     Corey Minyard <minyard@....org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Amol Grover <frextrite@...il.com>
Subject: [PATCH v3] drivers: char: ipmi: ipmi_msghandler: Pass lockdep expression to RCU lists

intf->cmd_rcvrs is traversed with list_for_each_entry_rcu
outside an RCU read-side critical section but under the
protection of intf->cmd_rcvrs_mutex.

ipmi_interfaces is traversed using list_for_each_entry_rcu
outside an RCU read-side critical section but under the protection
of ipmi_interfaces_mutex.

Hence, add the corresponding lockdep expression to the list traversal
primitive to silence false-positive lockdep warnings, and
harden RCU lists.

Add macro for the corresponding lockdep expression to make the code
clean and concise.

Signed-off-by: Amol Grover <frextrite@...il.com>
---
v3:
- Remove rcu_read_lock_held() from lockdep expression since it is
  implicitly checked.
- Remove unintended macro usage.
 
v2:
- Fix sparse error
  CHECK: Alignment should match open parenthesis

 drivers/char/ipmi/ipmi_msghandler.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index cad9563f8f48..64ba16dcb681 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -618,6 +618,8 @@ static DEFINE_MUTEX(ipmidriver_mutex);
 
 static LIST_HEAD(ipmi_interfaces);
 static DEFINE_MUTEX(ipmi_interfaces_mutex);
+#define ipmi_interfaces_mutex_held() \
+	lockdep_is_held(&ipmi_interfaces_mutex)
 static struct srcu_struct ipmi_interfaces_srcu;
 
 /*
@@ -1321,7 +1323,8 @@ static void _ipmi_destroy_user(struct ipmi_user *user)
 	 * synchronize_srcu()) then free everything in that list.
 	 */
 	mutex_lock(&intf->cmd_rcvrs_mutex);
-	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link) {
+	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link,
+				lockdep_is_held(&intf->cmd_rcvrs_mutex)) {
 		if (rcvr->user == user) {
 			list_del_rcu(&rcvr->link);
 			rcvr->next = rcvrs;
@@ -1599,7 +1602,8 @@ static struct cmd_rcvr *find_cmd_rcvr(struct ipmi_smi *intf,
 {
 	struct cmd_rcvr *rcvr;
 
-	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link) {
+	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link,
+				lockdep_is_held(&intf->cmd_rcvrs_mutex)) {
 		if ((rcvr->netfn == netfn) && (rcvr->cmd == cmd)
 					&& (rcvr->chans & (1 << chan)))
 			return rcvr;
@@ -1614,7 +1618,8 @@ static int is_cmd_rcvr_exclusive(struct ipmi_smi *intf,
 {
 	struct cmd_rcvr *rcvr;
 
-	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link) {
+	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link,
+				lockdep_is_held(&intf->cmd_rcvrs_mutex)) {
 		if ((rcvr->netfn == netfn) && (rcvr->cmd == cmd)
 					&& (rcvr->chans & chans))
 			return 0;
@@ -3450,7 +3455,8 @@ int ipmi_add_smi(struct module         *owner,
 	/* Look for a hole in the numbers. */
 	i = 0;
 	link = &ipmi_interfaces;
-	list_for_each_entry_rcu(tintf, &ipmi_interfaces, link) {
+	list_for_each_entry_rcu(tintf, &ipmi_interfaces, link,
+				ipmi_interfaces_mutex_held()) {
 		if (tintf->intf_num != i) {
 			link = &tintf->link;
 			break;
-- 
2.24.1