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Subject[PATCH 4.9 67/71] ip: use rb trees for IP frag queue.
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Oskolkov <posk@google.com>

(commit fa0f527358bd900ef92f925878ed6bfbd51305cc upstream)

Similar to TCP OOO RX queue, it makes sense to use rb trees to store
IP fragments, so that OOO fragments are inserted faster.

Tested:

- a follow-up patch contains a rather comprehensive ip defrag
self-test (functional)
- ran neper `udp_stream -c -H <host> -F 100 -l 300 -T 20`:
netstat --statistics
Ip:
282078937 total packets received
0 forwarded
0 incoming packets discarded
946760 incoming packets delivered
18743456 requests sent out
101 fragments dropped after timeout
282077129 reassemblies required
944952 packets reassembled ok
262734239 packet reassembles failed
(The numbers/stats above are somewhat better re:
reassemblies vs a kernel without this patchset. More
comprehensive performance testing TBD).

Reported-by: Jann Horn <jannh@google.com>
Reported-by: Juha-Matti Tilli <juha-matti.tilli@iki.fi>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/skbuff.h | 4
include/net/inet_frag.h | 3
net/ipv4/inet_fragment.c | 14 +-
net/ipv4/ip_fragment.c | 182 +++++++++++++++++---------------
net/ipv6/netfilter/nf_conntrack_reasm.c | 1
net/ipv6/reassembly.c | 1
6 files changed, 116 insertions(+), 89 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -643,14 +643,14 @@ struct sk_buff {
struct skb_mstamp skb_mstamp;
};
};
- struct rb_node rbnode; /* used in netem & tcp stack */
+ struct rb_node rbnode; /* used in netem, ip4 defrag, and tcp stack */
};

union {
+ struct sock *sk;
int ip_defrag_offset;
};

- struct sock *sk;
struct net_device *dev;

/*
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -74,7 +74,8 @@ struct inet_frag_queue {
struct timer_list timer;
spinlock_t lock;
atomic_t refcnt;
- struct sk_buff *fragments;
+ struct sk_buff *fragments; /* Used in IPv6. */
+ struct rb_root rb_fragments; /* Used in IPv4. */
struct sk_buff *fragments_tail;
ktime_t stamp;
int len;
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -136,12 +136,16 @@ void inet_frag_destroy(struct inet_frag_
fp = q->fragments;
nf = q->net;
f = nf->f;
- while (fp) {
- struct sk_buff *xp = fp->next;
+ if (fp) {
+ do {
+ struct sk_buff *xp = fp->next;

- sum_truesize += fp->truesize;
- kfree_skb(fp);
- fp = xp;
+ sum_truesize += fp->truesize;
+ kfree_skb(fp);
+ fp = xp;
+ } while (fp);
+ } else {
+ sum_truesize = skb_rbtree_purge(&q->rb_fragments);
}
sum = sum_truesize + f->qsize;

--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -134,7 +134,7 @@ static bool frag_expire_skip_icmp(u32 us
static void ip_expire(unsigned long arg)
{
const struct iphdr *iph;
- struct sk_buff *head;
+ struct sk_buff *head = NULL;
struct net *net;
struct ipq *qp;
int err;
@@ -150,14 +150,31 @@ static void ip_expire(unsigned long arg)

ipq_kill(qp);
__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
-
- head = qp->q.fragments;
-
__IP_INC_STATS(net, IPSTATS_MIB_REASMTIMEOUT);

- if (!(qp->q.flags & INET_FRAG_FIRST_IN) || !head)
+ if (!qp->q.flags & INET_FRAG_FIRST_IN)
goto out;

+ /* sk_buff::dev and sk_buff::rbnode are unionized. So we
+ * pull the head out of the tree in order to be able to
+ * deal with head->dev.
+ */
+ if (qp->q.fragments) {
+ head = qp->q.fragments;
+ qp->q.fragments = head->next;
+ } else {
+ head = skb_rb_first(&qp->q.rb_fragments);
+ if (!head)
+ goto out;
+ rb_erase(&head->rbnode, &qp->q.rb_fragments);
+ memset(&head->rbnode, 0, sizeof(head->rbnode));
+ barrier();
+ }
+ if (head == qp->q.fragments_tail)
+ qp->q.fragments_tail = NULL;
+
+ sub_frag_mem_limit(qp->q.net, head->truesize);
+
head->dev = dev_get_by_index_rcu(net, qp->iif);
if (!head->dev)
goto out;
@@ -177,16 +194,16 @@ static void ip_expire(unsigned long arg)
(skb_rtable(head)->rt_type != RTN_LOCAL))
goto out;

- skb_get(head);
spin_unlock(&qp->q.lock);
icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
- kfree_skb(head);
goto out_rcu_unlock;

out:
spin_unlock(&qp->q.lock);
out_rcu_unlock:
rcu_read_unlock();
+ if (head)
+ kfree_skb(head);
ipq_put(qp);
}

@@ -229,7 +246,7 @@ static int ip_frag_too_far(struct ipq *q
end = atomic_inc_return(&peer->rid);
qp->rid = end;

- rc = qp->q.fragments && (end - start) > max;
+ rc = qp->q.fragments_tail && (end - start) > max;

if (rc) {
struct net *net;
@@ -243,7 +260,6 @@ static int ip_frag_too_far(struct ipq *q

static int ip_frag_reinit(struct ipq *qp)
{
- struct sk_buff *fp;
unsigned int sum_truesize = 0;

if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
@@ -251,20 +267,14 @@ static int ip_frag_reinit(struct ipq *qp
return -ETIMEDOUT;
}

- fp = qp->q.fragments;
- do {
- struct sk_buff *xp = fp->next;
-
- sum_truesize += fp->truesize;
- kfree_skb(fp);
- fp = xp;
- } while (fp);
+ sum_truesize = skb_rbtree_purge(&qp->q.rb_fragments);
sub_frag_mem_limit(qp->q.net, sum_truesize);

qp->q.flags = 0;
qp->q.len = 0;
qp->q.meat = 0;
qp->q.fragments = NULL;
+ qp->q.rb_fragments = RB_ROOT;
qp->q.fragments_tail = NULL;
qp->iif = 0;
qp->ecn = 0;
@@ -276,7 +286,8 @@ static int ip_frag_reinit(struct ipq *qp
static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
{
struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
- struct sk_buff *prev, *next;
+ struct rb_node **rbn, *parent;
+ struct sk_buff *skb1;
struct net_device *dev;
unsigned int fragsize;
int flags, offset;
@@ -339,58 +350,58 @@ static int ip_frag_queue(struct ipq *qp,
if (err)
goto err;

- /* Find out which fragments are in front and at the back of us
- * in the chain of fragments so far. We must know where to put
- * this fragment, right?
- */
- prev = qp->q.fragments_tail;
- if (!prev || prev->ip_defrag_offset < offset) {
- next = NULL;
- goto found;
- }
- prev = NULL;
- for (next = qp->q.fragments; next != NULL; next = next->next) {
- if (next->ip_defrag_offset >= offset)
- break; /* bingo! */
- prev = next;
- }
+ /* Note : skb->rbnode and skb->dev share the same location. */
+ dev = skb->dev;
+ /* Makes sure compiler wont do silly aliasing games */
+ barrier();

-found:
/* RFC5722, Section 4, amended by Errata ID : 3089
* When reassembling an IPv6 datagram, if
* one or more its constituent fragments is determined to be an
* overlapping fragment, the entire datagram (and any constituent
* fragments) MUST be silently discarded.
*
- * We do the same here for IPv4.
+ * We do the same here for IPv4 (and increment an snmp counter).
*/

- /* Is there an overlap with the previous fragment? */
- if (prev &&
- (prev->ip_defrag_offset + prev->len) > offset)
- goto discard_qp;
-
- /* Is there an overlap with the next fragment? */
- if (next && next->ip_defrag_offset < end)
- goto discard_qp;
+ /* Find out where to put this fragment. */
+ skb1 = qp->q.fragments_tail;
+ if (!skb1) {
+ /* This is the first fragment we've received. */
+ rb_link_node(&skb->rbnode, NULL, &qp->q.rb_fragments.rb_node);
+ qp->q.fragments_tail = skb;
+ } else if ((skb1->ip_defrag_offset + skb1->len) < end) {
+ /* This is the common/special case: skb goes to the end. */
+ /* Detect and discard overlaps. */
+ if (offset < (skb1->ip_defrag_offset + skb1->len))
+ goto discard_qp;
+ /* Insert after skb1. */
+ rb_link_node(&skb->rbnode, &skb1->rbnode, &skb1->rbnode.rb_right);
+ qp->q.fragments_tail = skb;
+ } else {
+ /* Binary search. Note that skb can become the first fragment, but
+ * not the last (covered above). */
+ rbn = &qp->q.rb_fragments.rb_node;
+ do {
+ parent = *rbn;
+ skb1 = rb_to_skb(parent);
+ if (end <= skb1->ip_defrag_offset)
+ rbn = &parent->rb_left;
+ else if (offset >= skb1->ip_defrag_offset + skb1->len)
+ rbn = &parent->rb_right;
+ else /* Found an overlap with skb1. */
+ goto discard_qp;
+ } while (*rbn);
+ /* Here we have parent properly set, and rbn pointing to
+ * one of its NULL left/right children. Insert skb. */
+ rb_link_node(&skb->rbnode, parent, rbn);
+ }
+ rb_insert_color(&skb->rbnode, &qp->q.rb_fragments);

- /* Note : skb->ip_defrag_offset and skb->dev share the same location */
- dev = skb->dev;
if (dev)
qp->iif = dev->ifindex;
- /* Makes sure compiler wont do silly aliasing games */
- barrier();
skb->ip_defrag_offset = offset;

- /* Insert this fragment in the chain of fragments. */
- skb->next = next;
- if (!next)
- qp->q.fragments_tail = skb;
- if (prev)
- prev->next = skb;
- else
- qp->q.fragments = skb;
-
qp->q.stamp = skb->tstamp;
qp->q.meat += skb->len;
qp->ecn |= ecn;
@@ -412,7 +423,7 @@ found:
unsigned long orefdst = skb->_skb_refdst;

skb->_skb_refdst = 0UL;
- err = ip_frag_reasm(qp, prev, dev);
+ err = ip_frag_reasm(qp, skb, dev);
skb->_skb_refdst = orefdst;
return err;
}
@@ -429,15 +440,15 @@ err:
return err;
}

-
/* Build a new IP datagram from all its fragments. */
-
-static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
+static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
struct net_device *dev)
{
struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
struct iphdr *iph;
- struct sk_buff *fp, *head = qp->q.fragments;
+ struct sk_buff *fp, *head = skb_rb_first(&qp->q.rb_fragments);
+ struct sk_buff **nextp; /* To build frag_list. */
+ struct rb_node *rbn;
int len;
int ihlen;
int err;
@@ -451,25 +462,20 @@ static int ip_frag_reasm(struct ipq *qp,
goto out_fail;
}
/* Make the one we just received the head. */
- if (prev) {
- head = prev->next;
- fp = skb_clone(head, GFP_ATOMIC);
+ if (head != skb) {
+ fp = skb_clone(skb, GFP_ATOMIC);
if (!fp)
goto out_nomem;
-
- fp->next = head->next;
- if (!fp->next)
+ rb_replace_node(&skb->rbnode, &fp->rbnode, &qp->q.rb_fragments);
+ if (qp->q.fragments_tail == skb)
qp->q.fragments_tail = fp;
- prev->next = fp;
-
- skb_morph(head, qp->q.fragments);
- head->next = qp->q.fragments->next;
-
- consume_skb(qp->q.fragments);
- qp->q.fragments = head;
+ skb_morph(skb, head);
+ rb_replace_node(&head->rbnode, &skb->rbnode,
+ &qp->q.rb_fragments);
+ consume_skb(head);
+ head = skb;
}

- WARN_ON(!head);
WARN_ON(head->ip_defrag_offset != 0);

/* Allocate a new buffer for the datagram. */
@@ -494,24 +500,35 @@ static int ip_frag_reasm(struct ipq *qp,
clone = alloc_skb(0, GFP_ATOMIC);
if (!clone)
goto out_nomem;
- clone->next = head->next;
- head->next = clone;
skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
skb_frag_list_init(head);
for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
clone->len = clone->data_len = head->data_len - plen;
- head->data_len -= clone->len;
- head->len -= clone->len;
+ skb->truesize += clone->truesize;
clone->csum = 0;
clone->ip_summed = head->ip_summed;
add_frag_mem_limit(qp->q.net, clone->truesize);
+ skb_shinfo(head)->frag_list = clone;
+ nextp = &clone->next;
+ } else {
+ nextp = &skb_shinfo(head)->frag_list;
}

- skb_shinfo(head)->frag_list = head->next;
skb_push(head, head->data - skb_network_header(head));

- for (fp=head->next; fp; fp = fp->next) {
+ /* Traverse the tree in order, to build frag_list. */
+ rbn = rb_next(&head->rbnode);
+ rb_erase(&head->rbnode, &qp->q.rb_fragments);
+ while (rbn) {
+ struct rb_node *rbnext = rb_next(rbn);
+ fp = rb_to_skb(rbn);
+ rb_erase(rbn, &qp->q.rb_fragments);
+ rbn = rbnext;
+ *nextp = fp;
+ nextp = &fp->next;
+ fp->prev = NULL;
+ memset(&fp->rbnode, 0, sizeof(fp->rbnode));
head->data_len += fp->len;
head->len += fp->len;
if (head->ip_summed != fp->ip_summed)
@@ -522,7 +539,9 @@ static int ip_frag_reasm(struct ipq *qp,
}
sub_frag_mem_limit(qp->q.net, head->truesize);

+ *nextp = NULL;
head->next = NULL;
+ head->prev = NULL;
head->dev = dev;
head->tstamp = qp->q.stamp;
IPCB(head)->frag_max_size = max(qp->max_df_size, qp->q.max_size);
@@ -550,6 +569,7 @@ static int ip_frag_reasm(struct ipq *qp,

__IP_INC_STATS(net, IPSTATS_MIB_REASMOKS);
qp->q.fragments = NULL;
+ qp->q.rb_fragments = RB_ROOT;
qp->q.fragments_tail = NULL;
return 0;

--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -470,6 +470,7 @@ nf_ct_frag6_reasm(struct frag_queue *fq,
head->csum);

fq->q.fragments = NULL;
+ fq->q.rb_fragments = RB_ROOT;
fq->q.fragments_tail = NULL;

return true;
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -466,6 +466,7 @@ static int ip6_frag_reasm(struct frag_qu
__IP6_INC_STATS(net, __in6_dev_get(dev), IPSTATS_MIB_REASMOKS);
rcu_read_unlock();
fq->q.fragments = NULL;
+ fq->q.rb_fragments = RB_ROOT;
fq->q.fragments_tail = NULL;
return 1;


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