Patch "net: pktgen: remove rcu locking in pktgen_change_name()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

net: pktgen: remove rcu locking in pktgen_change_name()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-pktgen-remove-rcu-locking-in-pktgen_change_name.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Sat, 15 Oct 2016 17:50:49 +0200
Subject: net: pktgen: remove rcu locking in pktgen_change_name()

From: Eric Dumazet <[email protected]>

[ Upstream commit 9a0b1e8ba4061778897b544afc898de2163382f7 ]

After Jesper commit back in linux-3.18, we trigger a lockdep splat in proc_create_data() while allocating memory from pktgen_change_name().

This patch converts t->if_lock to a mutex, since it is now only used from control path, and adds proper locking to pktgen_change_name()

1) pktgen_thread_lock to protect the outer loop (iterating threads)
2) t->if_lock to protect the inner loop (iterating devices)

Note that before Jesper patch, pktgen_change_name() was lacking proper protection, but lockdep was not able to detect the problem.

---
 net/core/pktgen.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

@@ -215,8 +215,8 @@
 #define M_NETIF_RECEIVE 	1	/* Inject packets into stack */
 
 /* If lock -- protects updating of if_list */
-#define   if_lock(t)           spin_lock(&(t->if_lock));
-#define   if_unlock(t)           spin_unlock(&(t->if_lock));
+#define   if_lock(t)           mutex_lock(&(t->if_lock));
+#define   if_unlock(t)           mutex_unlock(&(t->if_lock));
 
 /* Used to help with determining the pkts on receive */
 #define PKTGEN_MAGIC 0xbe9be955

@@ -422,7 +422,7 @@ struct pktgen_net {
 };
 
 struct pktgen_thread {
-	spinlock_t if_lock;		/* for list of devices */
+	struct mutex if_lock;		/* for list of devices */
 	struct list_head if_list;	/* All device here */
 	struct list_head th_list;
 	struct task_struct *tsk;

@@ -2002,11 +2002,13 @@ static void pktgen_change_name(const str
 {
 	struct pktgen_thread *t;
 
+	mutex_lock(&pktgen_thread_lock);
+
 	list_for_each_entry(t, &pn->pktgen_threads, th_list) {
 		struct pktgen_dev *pkt_dev;
 
-		rcu_read_lock();
-		list_for_each_entry_rcu(pkt_dev, &t->if_list, list) {
+		if_lock(t);
+		list_for_each_entry(pkt_dev, &t->if_list, list) {
 			if (pkt_dev->odev != dev)
 				continue;
 

@@ -2021,8 +2023,9 @@ static void pktgen_change_name(const str
 				       dev->name);
 			break;
 		}
-		rcu_read_unlock();
+		if_unlock(t);
 	}
+	mutex_unlock(&pktgen_thread_lock);
 }
 
 static int pktgen_device_event(struct notifier_block *unused,

@@ -3726,7 +3729,7 @@ static int __net_init pktgen_create_thre
 		return -ENOMEM;
 	}
 
-	spin_lock_init(&t->if_lock);
+	mutex_init(&t->if_lock);
 	t->cpu = cpu;
 
 	INIT_LIST_HEAD(&t->if_list);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ipv4-use-the-right-lock-for-ping_group_range.patch queue-4.4/ipv4-disable-bh-in-set_ping_group_range.patch queue-4.4/tcp-fix-a-compile-error-in-dbgundo.patch queue-4.4/net-avoid-sk_forward_alloc-overflows.patch queue-4.4/udp-fix-ip_checksum-handling.patch queue-4.4/netlink-do-not-enter-direct-reclaim-from-netlink_dump.patch queue-4.4/ipv6-tcp-restore-ip6cb-for-pktoptions-skbs.patch queue-4.4/tcp-fix-overflow-in-__tcp_retransmit_skb.patch queue-4.4/packet-on-direct_xmit-limit-tso-and-csum-to-supported-devices.patch queue-4.4/net-pktgen-remove-rcu-locking-in-pktgen_change_name.patch