[3.13.y-ckt stable] Patch "net: call rcu_read_lock early in process_backlog" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Tue Sep 22 00:32:58 UTC 2015


This is a note to let you know that I have just added a patch titled

    net: call rcu_read_lock early in process_backlog

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt27.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 93a2b3b43c906dd65fa04eb33ad52ec90aaf8423 Mon Sep 17 00:00:00 2001
From: Julian Anastasov <ja at ssi.bg>
Date: Thu, 9 Jul 2015 09:59:10 +0300
Subject: net: call rcu_read_lock early in process_backlog

commit 2c17d27c36dcce2b6bf689f41a46b9e909877c21 upstream.

Incoming packet should be either in backlog queue or
in RCU read-side section. Otherwise, the final sequence of
flush_backlog() and synchronize_net() may miss packets
that can run without device reference:

CPU 1                  CPU 2
                       skb->dev: no reference
                       process_backlog:__skb_dequeue
                       process_backlog:local_irq_enable

on_each_cpu for
flush_backlog =>       IPI(hardirq): flush_backlog
                       - packet not found in backlog

                       CPU delayed ...
synchronize_net
- no ongoing RCU
read-side sections

netdev_run_todo,
rcu_barrier: no
ongoing callbacks
                       __netif_receive_skb_core:rcu_read_lock
                       - too late
free dev
                       process packet for freed dev

Fixes: 6e583ce5242f ("net: eliminate refcounting in backlog queue")
Cc: Eric W. Biederman <ebiederm at xmission.com>
Cc: Stephen Hemminger <stephen at networkplumber.org>
Signed-off-by: Julian Anastasov <ja at ssi.bg>
Signed-off-by: David S. Miller <davem at davemloft.net>
[ luis: backported to 3.16: used davem's backport to 3.18 ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/core/dev.c | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 870b9ec..6c97f06 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3534,8 +3534,6 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc)

 	pt_prev = NULL;

-	rcu_read_lock();
-
 another_round:
 	skb->skb_iif = skb->dev->ifindex;

@@ -3545,7 +3543,7 @@ another_round:
 	    skb->protocol == cpu_to_be16(ETH_P_8021AD)) {
 		skb = vlan_untag(skb);
 		if (unlikely(!skb))
-			goto unlock;
+			goto out;
 	}

 #ifdef CONFIG_NET_CLS_ACT
@@ -3570,7 +3568,7 @@ skip_taps:
 #ifdef CONFIG_NET_CLS_ACT
 	skb = handle_ing(skb, &pt_prev, &ret, orig_dev);
 	if (!skb)
-		goto unlock;
+		goto out;
 ncls:
 #endif

@@ -3585,7 +3583,7 @@ ncls:
 		if (vlan_do_receive(&skb))
 			goto another_round;
 		else if (unlikely(!skb))
-			goto unlock;
+			goto out;
 	}

 	rx_handler = rcu_dereference(skb->dev->rx_handler);
@@ -3597,7 +3595,7 @@ ncls:
 		switch (rx_handler(&skb)) {
 		case RX_HANDLER_CONSUMED:
 			ret = NET_RX_SUCCESS;
-			goto unlock;
+			goto out;
 		case RX_HANDLER_ANOTHER:
 			goto another_round;
 		case RX_HANDLER_EXACT:
@@ -3649,8 +3647,6 @@ drop:
 		ret = NET_RX_DROP;
 	}

-unlock:
-	rcu_read_unlock();
 out:
 	return ret;
 }
@@ -3697,29 +3693,30 @@ static int __netif_receive_skb(struct sk_buff *skb)
  */
 int netif_receive_skb(struct sk_buff *skb)
 {
+	int ret;
+
 	net_timestamp_check(netdev_tstamp_prequeue, skb);

 	if (skb_defer_rx_timestamp(skb))
 		return NET_RX_SUCCESS;

+	rcu_read_lock();
+
 #ifdef CONFIG_RPS
 	if (static_key_false(&rps_needed)) {
 		struct rps_dev_flow voidflow, *rflow = &voidflow;
-		int cpu, ret;
-
-		rcu_read_lock();
-
-		cpu = get_rps_cpu(skb->dev, skb, &rflow);
+		int cpu = get_rps_cpu(skb->dev, skb, &rflow);

 		if (cpu >= 0) {
 			ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
 			rcu_read_unlock();
 			return ret;
 		}
-		rcu_read_unlock();
 	}
 #endif
-	return __netif_receive_skb(skb);
+	ret = __netif_receive_skb(skb);
+	rcu_read_unlock();
+	return ret;
 }
 EXPORT_SYMBOL(netif_receive_skb);

@@ -4130,8 +4127,10 @@ static int process_backlog(struct napi_struct *napi, int quota)
 		unsigned int qlen;

 		while ((skb = __skb_dequeue(&sd->process_queue))) {
+			rcu_read_lock();
 			local_irq_enable();
 			__netif_receive_skb(skb);
+			rcu_read_unlock();
 			local_irq_disable();
 			input_queue_head_incr(sd);
 			if (++work >= quota) {
--
1.9.1





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