[PATCH 5.4 0/3] batman-adv: Fixes for stable/linux-4.19.y

[PATCH 5.4 0/3] batman-adv: Fixes for stable/linux-4.19.y

[Sven Eckelmann]

Hi,

I went through  all changes in batman-adv since v4.19 with a Fixes: line
and checked whether they were backported to the LTS kernels. The ones which
weren't ported and applied to this branch are now part of this patch series.

For this kernel version, I only found following three patches:

* batman-adv: Consider fragmentation for needed_headroom
* batman-adv: Reserve needed_*room for fragments
* batman-adv: Don't always reallocate the fragmentation skb head

which could in some circumstances cause packet loss but which were created
to fix high CPU load/low throughput problems. But I've added them here
anyway because the corresponding VXLAN patches were also added to stable.
And some stable kernels also got these fixes a while back.

Kind regards,
	Sven

Sven Eckelmann (3):
  batman-adv: Consider fragmentation for needed_headroom
  batman-adv: Reserve needed_*room for fragments
  batman-adv: Don't always reallocate the fragmentation skb head

 net/batman-adv/fragmentation.c  | 26 ++++++++++++++++----------
 net/batman-adv/hard-interface.c |  3 +++
 2 files changed, 19 insertions(+), 10 deletions(-)

-- 
2.30.2

[PATCH 5.4 1/3] batman-adv: Consider fragmentation for needed_headroom

[Sven Eckelmann]

commit 4ca23e2c2074465bff55ea14221175fecdf63c5f upstream.

If a batman-adv packets has to be fragmented, then the original batman-adv
packet header is not stripped away. Instead, only a new header is added in
front of the packet after it was split.

This size must be considered to avoid cost intensive reallocations during
the transmission through the various device layers.

Fixes: 7bca68c7844b ("batman-adv: Add lower layer needed_(head|tail)room to own ones")
Reported-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/hard-interface.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index afb52282d5bd..18e644f3cb30 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -554,6 +554,9 @@ static void batadv_hardif_recalc_extra_skbroom(struct net_device *soft_iface)
 	needed_headroom = lower_headroom + (lower_header_len - ETH_HLEN);
 	needed_headroom += batadv_max_header_len();
 
+	/* fragmentation headers don't strip the unicast/... header */
+	needed_headroom += sizeof(struct batadv_frag_packet);
+
 	soft_iface->needed_headroom = needed_headroom;
 	soft_iface->needed_tailroom = lower_tailroom;
 }
-- 
2.30.2

[PATCH 5.4 2/3] batman-adv: Reserve needed_*room for fragments

[Sven Eckelmann]

commit c5cbfc87558168ef4c3c27ce36eba6b83391db19 upstream.

The batadv net_device is trying to propagate the needed_headroom and
needed_tailroom from the lower devices. This is needed to avoid cost
intensive reallocations using pskb_expand_head during the transmission.

But the fragmentation code split the skb's without adding extra room at the
end/beginning of the various fragments. This reduced the performance of
transmissions over complex scenarios (batadv on vxlan on wireguard) because
the lower devices had to perform the reallocations at least once.

Fixes: ee75ed88879a ("batman-adv: Fragment and send skbs larger than mtu")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/fragmentation.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index 385fccdcf69d..f1d202ff396c 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -391,6 +391,7 @@ bool batadv_frag_skb_fwd(struct sk_buff *skb,
 
 /**
  * batadv_frag_create() - create a fragment from skb
+ * @net_dev: outgoing device for fragment
  * @skb: skb to create fragment from
  * @frag_head: header to use in new fragment
  * @fragment_size: size of new fragment
@@ -401,22 +402,25 @@ bool batadv_frag_skb_fwd(struct sk_buff *skb,
  *
  * Return: the new fragment, NULL on error.
  */
-static struct sk_buff *batadv_frag_create(struct sk_buff *skb,
+static struct sk_buff *batadv_frag_create(struct net_device *net_dev,
+					  struct sk_buff *skb,
 					  struct batadv_frag_packet *frag_head,
 					  unsigned int fragment_size)
 {
+	unsigned int ll_reserved = LL_RESERVED_SPACE(net_dev);
+	unsigned int tailroom = net_dev->needed_tailroom;
 	struct sk_buff *skb_fragment;
 	unsigned int header_size = sizeof(*frag_head);
 	unsigned int mtu = fragment_size + header_size;
 
-	skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
+	skb_fragment = dev_alloc_skb(ll_reserved + mtu + tailroom);
 	if (!skb_fragment)
 		goto err;
 
 	skb_fragment->priority = skb->priority;
 
 	/* Eat the last mtu-bytes of the skb */
-	skb_reserve(skb_fragment, header_size + ETH_HLEN);
+	skb_reserve(skb_fragment, ll_reserved + header_size);
 	skb_split(skb, skb_fragment, skb->len - fragment_size);
 
 	/* Add the header */
@@ -439,11 +443,12 @@ int batadv_frag_send_packet(struct sk_buff *skb,
 			    struct batadv_orig_node *orig_node,
 			    struct batadv_neigh_node *neigh_node)
 {
+	struct net_device *net_dev = neigh_node->if_incoming->net_dev;
 	struct batadv_priv *bat_priv;
 	struct batadv_hard_iface *primary_if = NULL;
 	struct batadv_frag_packet frag_header;
 	struct sk_buff *skb_fragment;
-	unsigned int mtu = neigh_node->if_incoming->net_dev->mtu;
+	unsigned int mtu = net_dev->mtu;
 	unsigned int header_size = sizeof(frag_header);
 	unsigned int max_fragment_size, num_fragments;
 	int ret;
@@ -503,7 +508,7 @@ int batadv_frag_send_packet(struct sk_buff *skb,
 			goto put_primary_if;
 		}
 
-		skb_fragment = batadv_frag_create(skb, &frag_header,
+		skb_fragment = batadv_frag_create(net_dev, skb, &frag_header,
 						  max_fragment_size);
 		if (!skb_fragment) {
 			ret = -ENOMEM;
-- 
2.30.2

[PATCH 5.4 3/3] batman-adv: Don't always reallocate the fragmentation skb head

[Sven Eckelmann]

commit 992b03b88e36254e26e9a4977ab948683e21bd9f upstream.

When a packet is fragmented by batman-adv, the original batman-adv header
is not modified. Only a new fragmentation is inserted between the original
one and the ethernet header. The code must therefore make sure that it has
a writable region of this size in the skbuff head.

But it is not useful to always reallocate the skbuff by this size even when
there would be more than enough headroom still in the skb. The reallocation
is just to costly during in this codepath.

Fixes: ee75ed88879a ("batman-adv: Fragment and send skbs larger than mtu")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/fragmentation.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index f1d202ff396c..0da90e73c79b 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -527,13 +527,14 @@ int batadv_frag_send_packet(struct sk_buff *skb,
 		frag_header.no++;
 	}
 
-	/* Make room for the fragment header. */
-	if (batadv_skb_head_push(skb, header_size) < 0 ||
-	    pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0) {
-		ret = -ENOMEM;
+	/* make sure that there is at least enough head for the fragmentation
+	 * and ethernet headers
+	 */
+	ret = skb_cow_head(skb, ETH_HLEN + header_size);
+	if (ret < 0)
 		goto put_primary_if;
-	}
 
+	skb_push(skb, header_size);
 	memcpy(skb->data, &frag_header, header_size);
 
 	/* Send the last fragment */
-- 
2.30.2

Re: [PATCH 5.4 0/3] batman-adv: Fixes for stable/linux-4.19.y

[Greg KH]

On Sat, Nov 20, 2021 at 01:40:50PM +0100, Sven Eckelmann wrote:
> Hi,
> 
> I went through  all changes in batman-adv since v4.19 with a Fixes: line
> and checked whether they were backported to the LTS kernels. The ones which
> weren't ported and applied to this branch are now part of this patch series.
> 
> For this kernel version, I only found following three patches:
> 
> * batman-adv: Consider fragmentation for needed_headroom
> * batman-adv: Reserve needed_*room for fragments
> * batman-adv: Don't always reallocate the fragmentation skb head
> 
> which could in some circumstances cause packet loss but which were created
> to fix high CPU load/low throughput problems. But I've added them here
> anyway because the corresponding VXLAN patches were also added to stable.
> And some stable kernels also got these fixes a while back.
> 
> Kind regards,
> 	Sven
> 
> Sven Eckelmann (3):
>   batman-adv: Consider fragmentation for needed_headroom
>   batman-adv: Reserve needed_*room for fragments
>   batman-adv: Don't always reallocate the fragmentation skb head

Now queued up, thanks.

greg k-h