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>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 68add55f8460fc19c1291e9a19d019d63edb2821..d21510d47aa22f0ec7896790566fb571af3da736 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -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);

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 06d044862e589ff05194d695bfdc610ed7e62195..ba08b78ed630c429ccf415af69bf27f2433af4f0 100644 (file)
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -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;

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 59cff7aa494efc83e3bd76f0cd748ebbbbac8910..e5387932c266e7e05eff7480857c290bdb7d28bb 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -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];
 

diff --git a/net/core/dev.c b/net/core/dev.c
index 8ea6b4b426116e216e8ade4466a281ce88299f04..1d75499add72b882a22dba7a6b5a2880e93a0a35 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -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);

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 29e34bc6a17ce913bdd0315258b3c1836b995386..74d3c36f8419b9082579d0907fcb5e890568b625 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -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;