From d0bf4a9e92b9a93ffeeacbd7b6cb83e0ee3dc2ef Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Mon, 29 Sep 2014 13:29:15 -0700
Subject: [PATCH] net: cleanup and document skb fclone layout
Lets use a proper structure to clearly document and implement
skb fast clones.
Then, we might experiment more easily alternative layouts.
This patch adds a new skb_fclone_busy() helper, used by tcp and xfrm,
to stop leaking of implementation details.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
include/linux/skbuff.h | 25 +++++++++++++++++++++++++
net/core/skbuff.c | 41 ++++++++++++++++++++---------------------
net/ipv4/tcp_output.c | 5 +----
net/xfrm/xfrm_policy.c | 4 +---
4 files changed, 47 insertions(+), 28 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 262efdbc346b..d8f7d74d5a4d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -781,6 +781,31 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
int *errcode,
gfp_t gfp_mask);
+/* Layout of fast clones : [skb1][skb2][fclone_ref] */
+struct sk_buff_fclones {
+ struct sk_buff skb1;
+
+ struct sk_buff skb2;
+
+ atomic_t fclone_ref;
+};
+
+/**
+ * skb_fclone_busy - check if fclone is busy
+ * @skb: buffer
+ *
+ * Returns true is skb is a fast clone, and its clone is not freed.
+ */
+static inline bool skb_fclone_busy(const struct sk_buff *skb)
+{
+ const struct sk_buff_fclones *fclones;
+
+ fclones = container_of(skb, struct sk_buff_fclones, skb1);
+
+ return skb->fclone == SKB_FCLONE_ORIG &&
+ fclones->skb2.fclone == SKB_FCLONE_CLONE;
+}
+
static inline struct sk_buff *alloc_skb_fclone(unsigned int size,
gfp_t priority)
{
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4be570a4ab21..a8cebb40699c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -257,15 +257,16 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
kmemcheck_annotate_variable(shinfo->destructor_arg);
if (flags & SKB_ALLOC_FCLONE) {
- struct sk_buff *child = skb + 1;
- atomic_t *fclone_ref = (atomic_t *) (child + 1);
+ struct sk_buff_fclones *fclones;
- kmemcheck_annotate_bitfield(child, flags1);
+ fclones = container_of(skb, struct sk_buff_fclones, skb1);
+
+ kmemcheck_annotate_bitfield(&fclones->skb2, flags1);
skb->fclone = SKB_FCLONE_ORIG;
- atomic_set(fclone_ref, 1);
+ atomic_set(&fclones->fclone_ref, 1);
- child->fclone = SKB_FCLONE_UNAVAILABLE;
- child->pfmemalloc = pfmemalloc;
+ fclones->skb2.fclone = SKB_FCLONE_UNAVAILABLE;
+ fclones->skb2.pfmemalloc = pfmemalloc;
}
out:
return skb;
@@ -524,8 +525,7 @@ static void skb_release_data(struct sk_buff *skb)
*/
static void kfree_skbmem(struct sk_buff *skb)
{
- struct sk_buff *other;
- atomic_t *fclone_ref;
+ struct sk_buff_fclones *fclones;
switch (skb->fclone) {
case SKB_FCLONE_UNAVAILABLE:
@@ -533,22 +533,21 @@ static void kfree_skbmem(struct sk_buff *skb)
break;
case SKB_FCLONE_ORIG:
- fclone_ref = (atomic_t *) (skb + 2);
- if (atomic_dec_and_test(fclone_ref))
- kmem_cache_free(skbuff_fclone_cache, skb);
+ fclones = container_of(skb, struct sk_buff_fclones, skb1);
+ if (atomic_dec_and_test(&fclones->fclone_ref))
+ kmem_cache_free(skbuff_fclone_cache, fclones);
break;
case SKB_FCLONE_CLONE:
- fclone_ref = (atomic_t *) (skb + 1);
- other = skb - 1;
+ fclones = container_of(skb, struct sk_buff_fclones, skb2);
/* The clone portion is available for
* fast-cloning again.
*/
skb->fclone = SKB_FCLONE_UNAVAILABLE;
- if (atomic_dec_and_test(fclone_ref))
- kmem_cache_free(skbuff_fclone_cache, other);
+ if (atomic_dec_and_test(&fclones->fclone_ref))
+ kmem_cache_free(skbuff_fclone_cache, fclones);
break;
}
}
@@ -859,17 +858,18 @@ EXPORT_SYMBOL_GPL(skb_copy_ubufs);
struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
{
- struct sk_buff *n;
+ struct sk_buff_fclones *fclones = container_of(skb,
+ struct sk_buff_fclones,
+ skb1);
+ struct sk_buff *n = &fclones->skb2;
if (skb_orphan_frags(skb, gfp_mask))
return NULL;
- n = skb + 1;
if (skb->fclone == SKB_FCLONE_ORIG &&
n->fclone == SKB_FCLONE_UNAVAILABLE) {
- atomic_t *fclone_ref = (atomic_t *) (n + 1);
n->fclone = SKB_FCLONE_CLONE;
- atomic_inc(fclone_ref);
+ atomic_inc(&fclones->fclone_ref);
} else {
if (skb_pfmemalloc(skb))
gfp_mask |= __GFP_MEMALLOC;
@@ -3240,8 +3240,7 @@ void __init skb_init(void)
SLAB_HWCACHE_ALIGN|SLAB_PANIC,
NULL);
skbuff_fclone_cache = kmem_cache_create("skbuff_fclone_cache",
- (2*sizeof(struct sk_buff)) +
- sizeof(atomic_t),
+ sizeof(struct sk_buff_fclones),
0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC,
NULL);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ee567e9e98c3..8d4eac793700 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2110,10 +2110,7 @@ bool tcp_schedule_loss_probe(struct sock *sk)
static bool skb_still_in_host_queue(const struct sock *sk,
const struct sk_buff *skb)
{
- const struct sk_buff *fclone = skb + 1;
-
- if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
- fclone->fclone == SKB_FCLONE_CLONE)) {
+ if (unlikely(skb_fclone_busy(skb))) {
NET_INC_STATS_BH(sock_net(sk),
LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
return true;
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index f623dca6ce30..4c4e457e7888 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1961,10 +1961,8 @@ static int xdst_queue_output(struct sock *sk, struct sk_buff *skb)
struct xfrm_dst *xdst = (struct xfrm_dst *) dst;
struct xfrm_policy *pol = xdst->pols[0];
struct xfrm_policy_queue *pq = &pol->polq;
- const struct sk_buff *fclone = skb + 1;
- if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
- fclone->fclone == SKB_FCLONE_CLONE)) {
+ if (unlikely(skb_fclone_busy(skb))) {
kfree_skb(skb);
return 0;
}