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From: Amol Grover <frextrite@gmail.com>
To: Corey Minyard <minyard@acm.org>, Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
	linux-kernel@vger.kernel.org,
	Joel Fernandes <joel@joelfernandes.org>,
	openipmi-developer@lists.sourceforge.net,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: [Linux-kernel-mentees] [PATCH] drivers: char: ipmi: ipmi_msghandler: Pass lockdep expression to RCU lists
Date: Fri, 10 Jan 2020 17:43:42 +0530
Message-ID: <20200110121341.31522-1-frextrite@gmail.com> (raw)

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@gmail.com>
---
 drivers/char/ipmi/ipmi_msghandler.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index cad9563f8f48..7eff0335bc82 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -35,6 +35,8 @@
 #include <linux/nospec.h>
 
 #define IPMI_DRIVER_VERSION "39.2"
+#define cmd_rcvrs_mutex_held() \
+	lockdep_is_held(&intf->cmd_rcvrs_mutex)
 
 static struct ipmi_recv_msg *ipmi_alloc_recv_msg(void);
 static int ipmi_init_msghandler(void);
@@ -618,6 +620,8 @@ 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 +1325,8 @@ 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,
+					cmd_rcvrs_mutex_held()) {
 		if (rcvr->user == user) {
 			list_del_rcu(&rcvr->link);
 			rcvr->next = rcvrs;
@@ -1599,7 +1604,8 @@ 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,
+			rcu_read_lock_held() || cmd_rcvrs_mutex_held()) {
 		if ((rcvr->netfn == netfn) && (rcvr->cmd == cmd)
 					&& (rcvr->chans & (1 << chan)))
 			return rcvr;
@@ -1614,7 +1620,8 @@ 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,
+					cmd_rcvrs_mutex_held()) {
 		if ((rcvr->netfn == netfn) && (rcvr->cmd == cmd)
 					&& (rcvr->chans & chans))
 			return 0;
@@ -3450,7 +3457,8 @@ 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

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