Re: [Bonding-devel] [v3 Patch 2/3] bridge: make bridge support netpoll

From: Cong Wang
Date: Tue Apr 13 2010 - 04:55:42 EST


Stephen Hemminger wrote:
On Mon, 12 Apr 2010 12:38:57 +0200
Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:

Le lundi 12 avril 2010 Ã 18:37 +0800, Cong Wang a Ãcrit :
Stephen Hemminger wrote:
There is no protection on dev->priv_flags for SMP access.
It would better bit value in dev->state if you are using it as control flag.

Then you could use if (unlikely(test_and_clear_bit(__IN_NETPOLL, &skb->dev->state)))
netpoll_send_skb(...)


Hmm, I think we can't use ->state here, it is not for this kind of purpose,
according to its comments.

Also, I find other usages of IFF_XXX flags of ->priv_flags are also using
&, | to set or clear the flags. So there must be some other things preventing
the race...
Yes, its RTNL that protects priv_flags changes, hopefully...


The patch was not protecting priv_flags with RTNL.
For example..


@@ -308,7 +312,9 @@ static void netpoll_send_skb(struct netp
tries > 0; --tries) {
if (__netif_tx_trylock(txq)) {
if (!netif_tx_queue_stopped(txq)) {
+ dev->priv_flags |= IFF_IN_NETPOLL;
status = ops->ndo_start_xmit(skb, dev);
+ dev->priv_flags &= ~IFF_IN_NETPOLL;
if (status == NETDEV_TX_OK)
txq_trans_update(txq);

Hmm, but I checked the bonding case (IFF_BONDING), it doesn't
hold rtnl_lock. Strange.

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