Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
From: Stephen Hemminger Date: Mon, 23 Mar 2009 15:45:17 -0700 > So you dynamically compute the additional space but if the space was > an awkward size, could it cause driver to breaks alignment assumptions? Yes, you'd need to 16-byte align or something like that. > And you didn't fixup the skb that is about to gag in the skb to make > more space, so transmitting device driver (gfar) is going to overwrite or die. This particular instance will do the headroom reallocation, that's unavoidable during the size transition event. The headroom checks can't ever be removed, but we won't hit them in the fast path after the adjustment is made by my patch. ___ Bridge mailing list Bridge@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/bridge
Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
On Mon, 23 Mar 2009 15:20:28 -0700 (PDT)
David Miller wrote:
> From: Stephen Hemminger
> Date: Mon, 23 Mar 2009 08:51:22 -0700
>
> > That ensures big enough header for locally generated packets, but
> > any drivers that need bigger headroom still must handle bridged packets
> > that come in with smaller space. When bridging packets, the skb comes
> > from the allocation by the receiving driver. Almost all drivers will
> > use dev_alloc_skb() which will allocate NET_SKB_PAD (16) bytes of
> > additional headroom. This is used to hold copy of ethernet header for
> > the bridge/netfilter code.
> >
> > So your patch is fine as an optimization but a driver can not safely
> > depend on any additional headroom. The driver must check if there
> > is space, and if no space is available, reallocate and copy.
>
> We had some plans to deal with this kind of issue for wireless
> too. Let me see if I can find the RFC patch from that discussion...
>
> Here it is, similar code would be added to the ipv4/ipv6 forwarding
> paths:
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 7c1d446..6c06fba 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -600,6 +600,7 @@ struct net_device
> * Cache line mostly used on receive path (including eth_type_trans())
> */
> unsigned long last_rx;/* Time of last Rx */
> + unsigned intrx_alloc_extra;
> /* Interface address info used in eth_type_trans() */
> unsigned char dev_addr[MAX_ADDR_LEN]; /* hw address, (before
> bcast
> because most packets
> are unicast) */
> diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
> index bdd7c35..531e483 100644
> --- a/net/bridge/br_forward.c
> +++ b/net/bridge/br_forward.c
> @@ -42,6 +42,22 @@ int br_dev_queue_push_xmit(struct sk_buff *skb)
> if (nf_bridge_maybe_copy_header(skb))
> kfree_skb(skb);
> else {
> + unsigned int headroom = skb_headroom(skb);
> + unsigned int hh_len = LL_RESERVED_SPACE(skb->dev);
> +
> + if (headroom < hh_len) {
> + struct net_device *in_dev;
> + unsigned int extra;
> +
> + in_dev = __dev_get_by_index(dev_net(skb->dev),
> + skb->iif);
> + BUG_ON(!in_dev);
> +
> + extra = hh_len - headroom;
> + if (extra >= in_dev->rx_alloc_extra)
> + in_dev->rx_alloc_extra = extra;
> + }
So you dynamically compute the additional space but if the space was
an awkward size, could it cause driver to breaks alignment assumptions?
And you didn't fixup the skb that is about to gag in the skb to make
more space, so transmitting device driver (gfar) is going to overwrite or die.
In summary, good idea, but may not solve the problem
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Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
From: Stephen Hemminger
Date: Mon, 23 Mar 2009 08:51:22 -0700
> That ensures big enough header for locally generated packets, but
> any drivers that need bigger headroom still must handle bridged packets
> that come in with smaller space. When bridging packets, the skb comes
> from the allocation by the receiving driver. Almost all drivers will
> use dev_alloc_skb() which will allocate NET_SKB_PAD (16) bytes of
> additional headroom. This is used to hold copy of ethernet header for
> the bridge/netfilter code.
>
> So your patch is fine as an optimization but a driver can not safely
> depend on any additional headroom. The driver must check if there
> is space, and if no space is available, reallocate and copy.
We had some plans to deal with this kind of issue for wireless
too. Let me see if I can find the RFC patch from that discussion...
Here it is, similar code would be added to the ipv4/ipv6 forwarding
paths:
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 7c1d446..6c06fba 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -600,6 +600,7 @@ struct net_device
* Cache line mostly used on receive path (including eth_type_trans())
*/
unsigned long last_rx;/* Time of last Rx */
+ unsigned intrx_alloc_extra;
/* Interface address info used in eth_type_trans() */
unsigned char dev_addr[MAX_ADDR_LEN]; /* hw address, (before
bcast
because most packets
are unicast) */
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index bdd7c35..531e483 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -42,6 +42,22 @@ int br_dev_queue_push_xmit(struct sk_buff *skb)
if (nf_bridge_maybe_copy_header(skb))
kfree_skb(skb);
else {
+ unsigned int headroom = skb_headroom(skb);
+ unsigned int hh_len = LL_RESERVED_SPACE(skb->dev);
+
+ if (headroom < hh_len) {
+ struct net_device *in_dev;
+ unsigned int extra;
+
+ in_dev = __dev_get_by_index(dev_net(skb->dev),
+ skb->iif);
+ BUG_ON(!in_dev);
+
+ extra = hh_len - headroom;
+ if (extra >= in_dev->rx_alloc_extra)
+ in_dev->rx_alloc_extra = extra;
+ }
+
skb_push(skb, ETH_HLEN);
dev_queue_xmit(skb);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 5c459f2..74a2515 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -255,11 +255,12 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev,
unsigned int length, gfp_t gfp_mask)
{
int node = dev->dev.parent ? dev_to_node(dev->dev.parent) : -1;
+ unsigned int extra = dev->rx_alloc_extra + NET_SKB_PAD;
struct sk_buff *skb;
- skb = __alloc_skb(length + NET_SKB_PAD, gfp_mask, 0, node);
+ skb = __alloc_skb(length + extra, gfp_mask, 0, node);
if (likely(skb)) {
- skb_reserve(skb, NET_SKB_PAD);
+ skb_reserve(skb, extra);
skb->dev = dev;
}
return skb;
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index f35eaea..86f0e36 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1562,13 +1562,13 @@ int ieee80211_subif_start_xmit(struct sk_buff *skb,
* be cloned. This could happen, e.g., with Linux bridge code passing
* us broadcast frames. */
- if (head_need > 0 || skb_cloned(skb)) {
+ if (head_need > 0 || skb_header_cloned(skb)) {
#if 0
printk(KERN_DEBUG "%s: need to reallocate buffer for %d bytes "
"of headroom\n", dev->name, head_need);
#endif
- if (skb_cloned(skb))
+ if (skb_header_cloned(skb))
I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
else
I802_DEBUG_INC(local->tx_expand_skb_head);
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Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
On Fri, 20 Mar 2009 17:04:29 +0800 Li Yang wrote: > The bridging device used a constant hard_header_len. This will cause > headroom shortage for ports with additional hardware header. The patch > makes bridging device to use the maximum value of all ports. > > Signed-off-by: Li Yang > --- That ensures big enough header for locally generated packets, but any drivers that need bigger headroom still must handle bridged packets that come in with smaller space. When bridging packets, the skb comes from the allocation by the receiving driver. Almost all drivers will use dev_alloc_skb() which will allocate NET_SKB_PAD (16) bytes of additional headroom. This is used to hold copy of ethernet header for the bridge/netfilter code. So your patch is fine as an optimization but a driver can not safely depend on any additional headroom. The driver must check if there is space, and if no space is available, reallocate and copy. ___ Bridge mailing list Bridge@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/bridge
Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
From: Li Yang Date: Mon, 23 Mar 2009 16:15:34 +0800 > I was wondering if this one failed to get your attention. yeah, happens all the time ___ Bridge mailing list Bridge@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/bridge
Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
On Mon, Mar 23, 2009 at 4:02 PM, David Miller wrote: > From: Li Yang > Date: Mon, 23 Mar 2009 15:59:24 +0800 > >> Any comment about this? Is it possible to be included in 2.6.29? > > Patience please? I reviewed and applied more than 80 patches > yesterday, maybe I'll get to your's after I recover from that. > > Your patch is in the queue at: > > http://patchwork.ozlabs.org/project/netdev/list/ > > You can monitor it's state and what's happening to it here. Good to know it is being tracked. After you have applied all those patches, I was wondering if this one failed to get your attention. Thanks. - Leo ___ Bridge mailing list Bridge@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/bridge
Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
From: Li Yang Date: Mon, 23 Mar 2009 15:59:24 +0800 > Any comment about this? Is it possible to be included in 2.6.29? Patience please? I reviewed and applied more than 80 patches yesterday, maybe I'll get to your's after I recover from that. Your patch is in the queue at: http://patchwork.ozlabs.org/project/netdev/list/ You can monitor it's state and what's happening to it here. ___ Bridge mailing list Bridge@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/bridge
Re: [Bridge] [PATCH] net/bridge: use the maximum hard_header_len of ports for bridging device
On Fri, Mar 20, 2009 at 5:04 PM, Li Yang wrote: > The bridging device used a constant hard_header_len. This will cause > headroom shortage for ports with additional hardware header. The patch > makes bridging device to use the maximum value of all ports. > > Signed-off-by: Li Yang > --- > Fixes the following BUG when using bridging with gianfar driver: > > skb_under_panic: text:c0224b84 len:122 put:8 head:dfb81800 data:dfb817fa > tail:0xdfb81874 end:0xdfb818a0 dev:eth1 > [ cut here ] > Kernel BUG at c02d9444 [verbose debug info unavailable] > Oops: Exception in kernel mode, sig: 5 [#1] > Call Trace: > [df2dbb20] [c02d9444] skb_under_panic+0x48/0x5c (unreliable) > [df2dbb30] [c0224b94] gfar_start_xmit+0x384/0x400 > [df2dbb60] [c02e1c8c] dev_hard_start_xmit+0x258/0x2cc > [df2dbba0] [c02f264c] __qdisc_run+0x5c/0x1f8 > [df2dbbd0] [c02e4bf4] dev_queue_xmit+0x264/0x2d0 > [df2dbbf0] [c036fdc8] br_dev_queue_push_xmit+0x90/0xf8 > [df2dbc00] [c036fcc8] br_flood+0xc8/0x120 > [df2dbc30] [c036ebe0] br_dev_xmit+0xbc/0xc0 > [df2dbc40] [c02e1c8c] dev_hard_start_xmit+0x258/0x2cc > [df2dbc80] [c02e4c04] dev_queue_xmit+0x274/0x2d0 > [df2dbca0] [c02ebaa8] neigh_resolve_output+0xfc/0x25c > Any comment about this? Is it possible to be included in 2.6.29? - Leo ___ Bridge mailing list Bridge@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/bridge
