Le jeudi 14 octobre 2010 à 05:00 +0100, Ben Hutchings a écrit :
> Beatrice Barbe reported a reproducible crash after creating large
> numbers of nested GRE tunnels and then pinging with the source address
> forced. I was able to reproduce this using net-2.6. I'm attaching the
> kernel config I used and a script to reproduce this based on the script
> she provided. The magic number of tunnels to create is apparently 37.
>
> With lockdep enabled, I get the following output:
>
Thats a known problem, actually, called stack exhaustion :)
net-next-2.6 contains a fix for this, adding the perc_cpu xmit_recursion
limit. We might push it to net-2.6
Thanks
commit 745e20f1b626b1be4b100af5d4bf7b3439392f8f
Author: Eric Dumazet <eric.duma...@gmail.com>
Date: Wed Sep 29 13:23:09 2010 -0700
net: add a recursion limit in xmit path
As tunnel devices are going to be lockless, we need to make sure a
misconfigured machine wont enter an infinite loop.
Add a percpu variable, and limit to three the number of stacked xmits.
Reported-by: Jesse Gross <je...@nicira.com>
Signed-off-by: Eric Dumazet <eric.duma...@gmail.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index 48ad47f..50dacca 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2177,6 +2177,9 @@ static inline int __dev_xmit_skb(struct sk_buff *skb,
struct Qdisc *q,
return rc;
}
+static DEFINE_PER_CPU(int, xmit_recursion);
+#define RECURSION_LIMIT 3
+
/**
* dev_queue_xmit - transmit a buffer
* @skb: buffer to transmit
@@ -2242,10 +2245,15 @@ int dev_queue_xmit(struct sk_buff *skb)
if (txq->xmit_lock_owner != cpu) {
+ if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT)
+ goto recursion_alert;
+
HARD_TX_LOCK(dev, txq, cpu);
if (!netif_tx_queue_stopped(txq)) {
+ __this_cpu_inc(xmit_recursion);
rc = dev_hard_start_xmit(skb, dev, txq);
+ __this_cpu_dec(xmit_recursion);
if (dev_xmit_complete(rc)) {
HARD_TX_UNLOCK(dev, txq);
goto out;
@@ -2257,7 +2265,9 @@ int dev_queue_xmit(struct sk_buff *skb)
"queue packet!\n", dev->name);
} else {
/* Recursion is detected! It is possible,
- * unfortunately */
+ * unfortunately
+ */
+recursion_alert:
if (net_ratelimit())
printk(KERN_CRIT "Dead loop on virtual device "
"%s, fix it urgently!\n", dev->name);
--
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