Patch "packet: Do not call fanout_release from atomic contexts" 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

packet: Do not call fanout_release from atomic contexts

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:
packet-do-not-call-fanout_release-from-atomic-contexts.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: Anoob Soman <[email protected]>
Date: Wed, 15 Feb 2017 20:25:39 +0000
Subject: packet: Do not call fanout_release from atomic contexts

From: Anoob Soman <[email protected]>

[ Upstream commit 2bd624b4611ffee36422782d16e1c944d1351e98 ]

Commit 6664498280cf ("packet: call fanout_release, while UNREGISTERING a netdev"), unfortunately, introduced the following issues.

1. calling mutex_lock(&fanout_mutex) (fanout_release()) from inside rcu_read-side critical section. rcu_read_lock disables preemption, most often, which prohibits calling sleeping functions.

[  ] include/linux/rcupdate.h:560 Illegal context switch in RCU read-side critical section!
[  ]
[  ] rcu_scheduler_active = 1, debug_locks = 0
[  ] 4 locks held by ovs-vswitchd/1969:
[  ]  #0:  (cb_lock){++++++}, at: [<ffffffff8158a6c9>] genl_rcv+0x19/0x40
[  ]  #1:  (ovs_mutex){+.+.+.}, at: [<ffffffffa04878ca>] ovs_vport_cmd_del+0x4a/0x100 [openvswitch]
[  ]  #2:  (rtnl_mutex){+.+.+.}, at: [<ffffffff81564157>] rtnl_lock+0x17/0x20
[  ]  #3:  (rcu_read_lock){......}, at: [<ffffffff81614165>] packet_notifier+0x5/0x3f0
[  ]
[  ] Call Trace:
[  ]  [<ffffffff813770c1>] dump_stack+0x85/0xc4
[  ]  [<ffffffff810c9077>] lockdep_rcu_suspicious+0x107/0x110
[  ]  [<ffffffff810a2da7>] ___might_sleep+0x57/0x210
[  ]  [<ffffffff810a2fd0>] __might_sleep+0x70/0x90
[  ]  [<ffffffff8162e80c>] mutex_lock_nested+0x3c/0x3a0
[  ]  [<ffffffff810de93f>] ? vprintk_default+0x1f/0x30
[  ]  [<ffffffff81186e88>] ? printk+0x4d/0x4f
[  ]  [<ffffffff816106dd>] fanout_release+0x1d/0xe0
[  ]  [<ffffffff81614459>] packet_notifier+0x2f9/0x3f0

2. calling mutex_lock(&fanout_mutex) inside spin_lock(&po->bind_lock). "sleeping function called from invalid context"

[  ] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:620
[  ] in_atomic(): 1, irqs_disabled(): 0, pid: 1969, name: ovs-vswitchd
[  ] INFO: lockdep is turned off.
[  ] Call Trace:
[  ]  [<ffffffff813770c1>] dump_stack+0x85/0xc4
[  ]  [<ffffffff810a2f52>] ___might_sleep+0x202/0x210
[  ]  [<ffffffff810a2fd0>] __might_sleep+0x70/0x90
[  ]  [<ffffffff8162e80c>] mutex_lock_nested+0x3c/0x3a0
[  ]  [<ffffffff816106dd>] fanout_release+0x1d/0xe0
[  ]  [<ffffffff81614459>] packet_notifier+0x2f9/0x3f0

3. calling dev_remove_pack(&fanout->prot_hook), from inside spin_lock(&po->bind_lock) or rcu_read-side critical-section. dev_remove_pack() -> synchronize_net(), which might sleep.

[  ] BUG: scheduling while atomic: ovs-vswitchd/1969/0x00000002
[  ] INFO: lockdep is turned off.
[  ] Call Trace:
[  ]  [<ffffffff813770c1>] dump_stack+0x85/0xc4
[  ]  [<ffffffff81186274>] __schedule_bug+0x64/0x73
[  ]  [<ffffffff8162b8cb>] __schedule+0x6b/0xd10
[  ]  [<ffffffff8162c5db>] schedule+0x6b/0x80
[  ]  [<ffffffff81630b1d>] schedule_timeout+0x38d/0x410
[  ]  [<ffffffff810ea3fd>] synchronize_sched_expedited+0x53d/0x810
[  ]  [<ffffffff810ea6de>] synchronize_rcu_expedited+0xe/0x10
[  ]  [<ffffffff8154eab5>] synchronize_net+0x35/0x50
[  ]  [<ffffffff8154eae3>] dev_remove_pack+0x13/0x20
[  ]  [<ffffffff8161077e>] fanout_release+0xbe/0xe0
[  ]  [<ffffffff81614459>] packet_notifier+0x2f9/0x3f0

4. fanout_release() races with calls from different CPU.

To fix the above problems, remove the call to fanout_release() under rcu_read_lock(). Instead, call __dev_remove_pack(&fanout->prot_hook) and netdev_run_todo will be happy that &dev->ptype_specific list is empty. In order to achieve this, I moved dev_{add,remove}_pack() out of fanout_{add,release} to __fanout_{link,unlink}. So, call to {,__}unregister_prot_hook() will make sure fanout->prot_hook is removed as well.

---
 net/packet/af_packet.c |   31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

@@ -1497,6 +1497,8 @@ static void __fanout_link(struct sock *s
 	f->arr[f->num_members] = sk;
 	smp_wmb();
 	f->num_members++;
+	if (f->num_members == 1)
+		dev_add_pack(&f->prot_hook);
 	spin_unlock(&f->lock);
 }
 

@@ -1513,6 +1515,8 @@ static void __fanout_unlink(struct sock
 	BUG_ON(i >= f->num_members);
 	f->arr[i] = f->arr[f->num_members - 1];
 	f->num_members--;
+	if (f->num_members == 0)
+		__dev_remove_pack(&f->prot_hook);
 	spin_unlock(&f->lock);
 }
 

@@ -1697,7 +1701,6 @@ static int fanout_add(struct sock *sk, u
 		match->prot_hook.func = packet_rcv_fanout;
 		match->prot_hook.af_packet_priv = match;
 		match->prot_hook.id_match = match_fanout_group;
-		dev_add_pack(&match->prot_hook);
 		list_add(&match->list, &fanout_list);
 	}
 	err = -EINVAL;

@@ -1722,7 +1725,12 @@ out:
 	return err;
 }
 
-static void fanout_release(struct sock *sk)
+/* If pkt_sk(sk)->fanout->sk_ref is zero, this function removes
+ * pkt_sk(sk)->fanout from fanout_list and returns pkt_sk(sk)->fanout.
+ * It is the responsibility of the caller to call fanout_release_data() and
+ * free the returned packet_fanout (after synchronize_net())
+ */
+static struct packet_fanout *fanout_release(struct sock *sk)
 {
 	struct packet_sock *po = pkt_sk(sk);
 	struct packet_fanout *f;

@@ -1732,17 +1740,17 @@ static void fanout_release(struct sock *
 	if (f) {
 		po->fanout = NULL;
 
-		if (atomic_dec_and_test(&f->sk_ref)) {
+		if (atomic_dec_and_test(&f->sk_ref))
 			list_del(&f->list);
-			dev_remove_pack(&f->prot_hook);
-			fanout_release_data(f);
-			kfree(f);
-		}
+		else
+			f = NULL;
 
 		if (po->rollover)
 			kfree_rcu(po->rollover, rcu);
 	}
 	mutex_unlock(&fanout_mutex);
+
+	return f;
 }
 
 static bool packet_extra_vlan_len_allowed(const struct net_device *dev,

@@ -2851,6 +2859,7 @@ static int packet_release(struct socket
 {
 	struct sock *sk = sock->sk;
 	struct packet_sock *po;
+	struct packet_fanout *f;
 	struct net *net;
 	union tpacket_req_u req_u;
 

@@ -2890,9 +2899,14 @@ static int packet_release(struct socket
 		packet_set_ring(sk, &req_u, 1, 1);
 	}
 
-	fanout_release(sk);
+	f = fanout_release(sk);
 
 	synchronize_net();
+
+	if (f) {
+		fanout_release_data(f);
+		kfree(f);
+	}
 	/*
 	 *	Now the socket is dead. No more input will appear.
 	 */

@@ -3866,7 +3880,6 @@ static int packet_notifier(struct notifi
 				}
 				if (msg == NETDEV_UNREGISTER) {
 					packet_cached_dev_reset(po);
-					fanout_release(sk);
 					po->ifindex = -1;
 					if (po->prot_hook.dev)
 						dev_put(po->prot_hook.dev);

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

queue-4.4/packet-do-not-call-fanout_release-from-atomic-contexts.patch