netdev - Re: macvtap bug: using smp_processor

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Date:	Thu, 08 Aug 2013 06:21:12 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Thomas Huth <thuth@...ux.vnet.ibm.com>
Cc:	netdev@...r.kernel.org, Vlad Yasevich <vyasevic@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: macvtap bug: using smp_processor_id() in preemptible code

On Thu, 2013-08-08 at 10:25 +0200, Thomas Huth wrote:
> Hi,

> Thank you very much for your fast reply and the fix, it indeed fixes
> the messages about macvtap_do_read!
> However, I now noticed that there are more messages, which I just did
> not see before because my dmesg output was already flooded with the
> messages about macvtap_do_read. The other messages are all about
> macvlan_start_xmit:
> 
> BUG: using smp_processor_id() in preemptible [00000000] code: vhost-45897/45898
> caller is macvlan_start_xmit+0x10a/0x1b4 [macvlan]
> CPU: 1 PID: 45898 Comm: vhost-45897 Not tainted 3.11.0-bisecttest #16
>        00000001189b3960 00000001189b3970 0000000000000002 0000000000000000 
>        00000001189b3a00 00000001189b3978 00000001189b3978 00000000001127b4 
>        0000000000000000 0000000000000001 0000000000000000 000000000000000b 
>        0000000000000060 000003fe00000008 0000000000000000 00000001189b39d0 
>        00000000006ea2f0 00000000001127b4 00000001189b3960 00000001189b39b0 
> Call Trace:
> ([<00000000001126ee>] show_trace+0x126/0x144)
>  [<00000000001127d2>] show_stack+0xc6/0xd4
>  [<000000000068bdb8>] dump_stack+0x74/0xd4
>  [<0000000000481132>] debug_smp_processor_id+0xf6/0x114
>  [<000003ff802b72ca>] macvlan_start_xmit+0x10a/0x1b4 [macvlan]
>  [<000003ff802ea69a>] macvtap_get_user+0x982/0xbc4 [macvtap]
>  [<000003ff802ea92a>] macvtap_sendmsg+0x4e/0x60 [macvtap]
>  [<000003ff8031947c>] handle_tx+0x494/0x5ec [vhost_net]
>  [<000003ff8028f77c>] vhost_worker+0x15c/0x1c4 [vhost]
>  [<000000000015f3ac>] kthread+0xd8/0xe4
>  [<000000000069356e>] kernel_thread_starter+0x6/0xc
>  [<0000000000693568>] kernel_thread_starter+0x0/0xc
> 2 locks held by vhost-45897/45898:
>  #0:  (&vq->mutex){+.+.+.}, at: [<000003ff8031903c>] handle_tx+0x54/0x5ec [vhost_net]
>  #1:  (rcu_read_lock){.+.+..}, at: [<000003ff802ea53c>] macvtap_get_user+0x824/0xbc4 [macvtap]
> 
> Do you also have got an idea how to silence these messages?

Sure, please try following cumulative patch, thanks !

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index a98fb0e..b51db2a 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -818,10 +818,13 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
 		skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
 		skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
 	}
-	if (vlan)
+	if (vlan) {
+		local_bh_disable();
 		macvlan_start_xmit(skb, vlan->dev);
-	else
+		local_bh_enable();
+	} else {
 		kfree_skb(skb);
+	}
 	rcu_read_unlock();
 
 	return total_len;
@@ -912,8 +915,11 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
 done:
 	rcu_read_lock();
 	vlan = rcu_dereference(q->vlan);
-	if (vlan)
+	if (vlan) {
+		preempt_disable();
 		macvlan_count_rx(vlan, copied - vnet_hdr_len, ret == 0, 0);
+		preempt_enable();
+	}
 	rcu_read_unlock();
 
 	return ret ? ret : copied;


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