Subject: Re: NULL deref in bnx2 / crashes ? ( was: netconsole leads to stalled CPU task )

From: Cong Wang <[email-masked]>
Date: Thu, 23 Aug 2012 08:31:14 +0000 (UTC)

On Thu, 23 Aug 2012 at 07:57 GMT, Cong Wang <[email-masked]> wrote:
> On Wed, 22 Aug 2012 at 14:29 GMT, Sylvain Munaut <[email-masked]> wrote:
>> Hi,
>>
>>
>> The machine with the intel card still hard freeze (no output / no nothing ...)
>> The machine with the bnx2 don't crash anymore and no NULL deref, but
>> the modprobe still hangs and I get this every 180 sec or so :
>
> The NULL-deref can be reproduced easily, and Eric's patch could fix it.
> So, Eric, can you resend your patch with your SOB?
>
> I can't reproduce the hang as it is net driver specific, it is
> probably related with my patch:
>
> commit 6bdb7fe31046ac50b47e83c35cd6c6b6160a475d
> Author: Amerigo Wang <[email-masked]>
> Date:   Fri Aug 10 01:24:50 2012 +0000
>
>     netpoll: re-enable irq in poll_napi()
>

Could you test the following patch?

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index ddc453b..ed4d1e4 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -166,11 +166,18 @@ static int poll_one_napi(struct netpoll_info *npinfo,
 static void poll_napi(struct net_device *dev)
 {
 	struct napi_struct *napi;
+	LIST_HEAD(napi_list);
 	int budget = 16;
 
 	WARN_ON_ONCE(!irqs_disabled());
 
-	list_for_each_entry(napi, &dev->napi_list, dev_list) {
+	/* After we enable the IRQ, new entries could be added
+	 * to this list, we need to save it before re-enable
+	 * IRQ.
+	 */
+	list_splice_tail(&dev->napi_list, &napi_list);
+
+	list_for_each_entry(napi, &napi_list, dev_list) {
 		local_irq_enable();
 		if (napi->poll_owner != smp_processor_id() &&
 		    spin_trylock(&napi->poll_lock)) {
@@ -187,6 +194,7 @@ static void poll_napi(struct net_device *dev)
 		}
 		local_irq_disable();
 	}
+	list_splice_tail(&napi_list, &dev->napi_list);
 }
 
 static void service_arp_queue(struct netpoll_info *npi)

However, it seems we should take rtnl lock to make sure dev->napi_list
is really safe, I am not sure if the following one makes sense.

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index ddc453b..7770e2b 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -170,8 +170,9 @@ static void poll_napi(struct net_device *dev)
 
 	WARN_ON_ONCE(!irqs_disabled());
 
+	local_irq_enable();
+	rtnl_lock();
 	list_for_each_entry(napi, &dev->napi_list, dev_list) {
-		local_irq_enable();
 		if (napi->poll_owner != smp_processor_id() &&
 		    spin_trylock(&napi->poll_lock)) {
 			rcu_read_lock_bh();
@@ -180,13 +181,12 @@ static void poll_napi(struct net_device *dev)
 			rcu_read_unlock_bh();
 			spin_unlock(&napi->poll_lock);
 
-			if (!budget) {
-				local_irq_disable();
+			if (!budget)
 				break;
-			}
 		}
-		local_irq_disable();
 	}
+	rtnl_unlock();
+	local_irq_disable();
 }
 
 static void service_arp_queue(struct netpoll_info *npi)