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sock: enable MSG_ZEROCOPY 

Prepare the datapath for refcounted ubuf_info. Clone ubuf_info with
skb_zerocopy_clone() wherever needed due to skb split, merge, resize
or clone.

Split skb_orphan_frags into two variants. The split, merge, .. paths
support reference counted zerocopy buffers, so do not do a deep copy.
Add skb_orphan_frags_rx for paths that may loop packets to receive
sockets. That is not allowed, as it may cause unbounded latency.
Deep copy all zerocopy copy buffers, ref-counted or not, in this path.

The exact locations to modify were chosen by exhaustively searching
through all code that might modify skb_frag references and/or the
the SKBTX_DEV_ZEROCOPY tx_flags bit.

The changes err on the safe side, in two ways.

(1) legacy ubuf_info paths virtio and tap are not modified. They keep
    a 1:1 ubuf_info to sk_buff relationship. Calls to skb_orphan_frags
    still call skb_copy_ubufs and thus copy frags in this case.

(2) not all copies deep in the stack are addressed yet. skb_shift,
    skb_split and skb_try_coalesce can be refined to avoid copying.
    These are not in the hot path and this patch is hairy enough as
    is, so that is left for future refinement.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willem de Bruijn 2017-08-03 16:29:41 -04:00 committed by David S. Miller
parent 76851d1212
commit 1f8b977ab3
5 changed files with 36 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/tun.c
View File

@ -892,7 +892,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
sk_filter(tfile->socket.sk, skb))
goto drop;
if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC)))
goto drop;
skb_tx_timestamp(skb);

1
drivers/vhost/net.c
View File

@ -533,6 +533,7 @@ static void handle_tx(struct vhost_net *net)
ubuf->callback = vhost_zerocopy_callback;
ubuf->ctx = nvq->ubufs;
ubuf->desc = nvq->upend_idx;
atomic_set(&ubuf->refcnt, 1);
msg.msg_control = ubuf;
msg.msg_controllen = sizeof(ubuf);
ubufs = nvq->ubufs;

14
include/linux/skbuff.h
View File

@ -2512,7 +2512,17 @@ static inline void skb_orphan(struct sk_buff *skb)
*/
static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
{
if (likely(!(skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY)))
if (likely(!skb_zcopy(skb)))
return 0;
if (skb_uarg(skb)->callback == sock_zerocopy_callback)
return 0;
return skb_copy_ubufs(skb, gfp_mask);
}
/* Frags must be orphaned, even if refcounted, if skb might loop to rx path */
static inline int skb_orphan_frags_rx(struct sk_buff *skb, gfp_t gfp_mask)
{
if (likely(!skb_zcopy(skb)))
return 0;
return skb_copy_ubufs(skb, gfp_mask);
}
@ -2944,6 +2954,8 @@ static inline int skb_add_data(struct sk_buff *skb,
static inline bool skb_can_coalesce(struct sk_buff *skb, int i,
const struct page *page, int off)
{
if (skb_zcopy(skb))
return false;
if (i) {
const struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[i - 1];

4
net/core/dev.c
View File

@ -1853,7 +1853,7 @@ static inline int deliver_skb(struct sk_buff *skb,
struct packet_type *pt_prev,
struct net_device *orig_dev)
{
if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC)))
return -ENOMEM;
refcount_inc(&skb->users);
return pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
@ -4412,7 +4412,7 @@ skip_classify:
}
if (pt_prev) {
if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
if (unlikely(skb_orphan_frags_rx(skb, GFP_ATOMIC)))
goto drop;
else
ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev);

48
net/core/skbuff.c
View File

@ -567,21 +567,10 @@ static void skb_release_data(struct sk_buff *skb)
for (i = 0; i < shinfo->nr_frags; i++)
__skb_frag_unref(&shinfo->frags[i]);
/*
* If skb buf is from userspace, we need to notify the caller
* the lower device DMA has done;
*/
if (shinfo->tx_flags & SKBTX_DEV_ZEROCOPY) {
struct ubuf_info *uarg;
uarg = shinfo->destructor_arg;
if (uarg->callback)
uarg->callback(uarg, true);
}
if (shinfo->frag_list)
kfree_skb_list(shinfo->frag_list);
skb_zcopy_clear(skb, true);
skb_free_head(skb);
}
@ -695,14 +684,7 @@ EXPORT_SYMBOL(kfree_skb_list);
*/
void skb_tx_error(struct sk_buff *skb)
{
if (skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
struct ubuf_info *uarg;
uarg = skb_shinfo(skb)->destructor_arg;
if (uarg->callback)
uarg->callback(uarg, false);
skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
}
skb_zcopy_clear(skb, true);
}
EXPORT_SYMBOL(skb_tx_error);
@ -1029,9 +1011,7 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
}
EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream);
/* unused only until next patch in the series; will remove attribute */
static int __attribute__((unused))
skb_zerocopy_clone(struct sk_buff *nskb, struct sk_buff *orig,
static int skb_zerocopy_clone(struct sk_buff *nskb, struct sk_buff *orig,
gfp_t gfp_mask)
{
if (skb_zcopy(orig)) {
@ -1068,7 +1048,6 @@ static int __attribute__((unused))
*/
int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
{
struct ubuf_info *uarg = skb_shinfo(skb)->destructor_arg;
int num_frags = skb_shinfo(skb)->nr_frags;
struct page *page, *head = NULL;
int i, new_frags;
@ -1127,8 +1106,6 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
for (i = 0; i < num_frags; i++)
skb_frag_unref(skb, i);
uarg->callback(uarg, false);
/* skb frags point to kernel buffers */
for (i = 0; i < new_frags - 1; i++) {
__skb_fill_page_desc(skb, i, head, 0, PAGE_SIZE);
@ -1137,7 +1114,7 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
__skb_fill_page_desc(skb, new_frags - 1, head, 0, d_off);
skb_shinfo(skb)->nr_frags = new_frags;
skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
skb_zcopy_clear(skb, false);
return 0;
}
EXPORT_SYMBOL_GPL(skb_copy_ubufs);
@ -1298,7 +1275,8 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
if (skb_shinfo(skb)->nr_frags) {
int i;
if (skb_orphan_frags(skb, gfp_mask)) {
if (skb_orphan_frags(skb, gfp_mask) ||
skb_zerocopy_clone(n, skb, gfp_mask)) {
kfree_skb(n);
n = NULL;
goto out;
@ -1375,9 +1353,10 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
* be since all we did is relocate the values
*/
if (skb_cloned(skb)) {
/* copy this zero copy skb frags */
if (skb_orphan_frags(skb, gfp_mask))
goto nofrags;
if (skb_zcopy(skb))
atomic_inc(&skb_uarg(skb)->refcnt);
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
skb_frag_ref(skb, i);
@ -1872,6 +1851,9 @@ end:
skb->tail += delta;
skb->data_len -= delta;
if (!skb->data_len)
skb_zcopy_clear(skb, false);
return skb_tail_pointer(skb);
}
EXPORT_SYMBOL(__pskb_pull_tail);
@ -2627,6 +2609,7 @@ skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
skb_tx_error(from);
return -ENOMEM;
}
skb_zerocopy_clone(to, from, GFP_ATOMIC);
for (i = 0; i < skb_shinfo(from)->nr_frags; i++) {
if (!len)
@ -2924,6 +2907,7 @@ void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len)
skb_shinfo(skb1)->tx_flags |= skb_shinfo(skb)->tx_flags &
SKBTX_SHARED_FRAG;
skb_zerocopy_clone(skb1, skb, 0);
if (len < pos) /* Split line is inside header. */
skb_split_inside_header(skb, skb1, len, pos);
else /* Second chunk has no header, nothing to copy. */
@ -2967,6 +2951,8 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
if (skb_headlen(skb))
return 0;
if (skb_zcopy(tgt) || skb_zcopy(skb))
return 0;
todo = shiftlen;
from = 0;
@ -3540,6 +3526,8 @@ normal:
skb_shinfo(nskb)->tx_flags |= skb_shinfo(head_skb)->tx_flags &
SKBTX_SHARED_FRAG;
if (skb_zerocopy_clone(nskb, head_skb, GFP_ATOMIC))
goto err;
while (pos < offset + len) {
if (i >= nfrags) {
@ -4663,6 +4651,8 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
if (skb_has_frag_list(to) || skb_has_frag_list(from))
return false;
if (skb_zcopy(to) || skb_zcopy(from))
return false;
if (skb_headlen(from) != 0) {
struct page *page;