[PATCH 3.4 020/107] net: call rcu_read_lock early in process_backlog

lizf
2016-03-16T08:08:36Z

From: Julian Anastasov <ja@ssi.bg>

3.4.111-rc1 review patch. If anyone has any objections, please let me know.

------------------

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@xmission.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>
[lizf: Backported to 3.4:
- adjust context
- no need to change "goto unlock" to "goto out"]
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
net/core/dev.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 1e363d0..4f679bf 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3191,8 +3191,6 @@ static int __netif_receive_skb(struct sk_buff *skb)

pt_prev = NULL;

- rcu_read_lock();
-
another_round:

__this_cpu_inc(softnet_data.processed);
@@ -3287,7 +3285,6 @@ ncls:
}

out:
- rcu_read_unlock();
return ret;
}

@@ -3308,29 +3305,30 @@ out:
*/
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);

@@ -3721,8 +3719,10 @@ 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