[05/12,v2,RFC] skbuff: replace sock_zerocopy_put() with skb_zcopy_put()

Commit Message

Jonathan Lemon Dec. 22, 2020, 12:09 a.m. UTC

From: Jonathan Lemon <[e-mail]>

Replace sock_zerocopy_put with the generic skb_zcopy_put()
function.  Pass 'true' as the success argument, as this
is identical to no change.

Signed-off-by: Jonathan Lemon <[e-mail]>
---
 include/linux/skbuff.h | 7 ++++++-
 net/core/skbuff.c      | 9 +--------
 net/ipv4/tcp.c         | 2 +-
 3 files changed, 8 insertions(+), 10 deletions(-)

Comments

Willem de Bruijn Dec. 22, 2020, 2:42 p.m. UTC | #1

On Mon, Dec 21, 2020 at 7:09 PM Jonathan Lemon <[e-mail]> wrote:
>
> From: Jonathan Lemon <[e-mail]>
>
> Replace sock_zerocopy_put with the generic skb_zcopy_put()
> function.  Pass 'true' as the success argument, as this
> is identical to no change.
>
> Signed-off-by: Jonathan Lemon <[e-mail]>

uarg->zerocopy may be false if sock_zerocopy_put_abort is called from
tcp_sendmsg_locked

Jonathan Lemon Dec. 22, 2020, 5:19 p.m. UTC | #2

On Tue, Dec 22, 2020 at 09:42:40AM -0500, Willem de Bruijn wrote:
> On Mon, Dec 21, 2020 at 7:09 PM Jonathan Lemon <[e-mail]> wrote:
> >
> > From: Jonathan Lemon <[e-mail]>
> >
> > Replace sock_zerocopy_put with the generic skb_zcopy_put()
> > function.  Pass 'true' as the success argument, as this
> > is identical to no change.
> >
> > Signed-off-by: Jonathan Lemon <[e-mail]>
> 
> uarg->zerocopy may be false if sock_zerocopy_put_abort is called from
> tcp_sendmsg_locked

Yes, it may well be false.  The original logic goes:

   sock_zerocopy_put_abort()
   sock_zerocopy_put()
   sock_zerocopy_callback(..., success = uarg->zerocopy)
     if (success)

The new logic is now:

   sock_zerocopy_put_abort()
   sock_zerocopy_callback(..., success = true)
     uarg->zerocopy = uarg->zerocopy & success
     if (uarg->zerocopy)

The success value ls latched into uarg->zerocopy, and any failure
is persistent.  Hence my comment about passing 'true' not changing
the logic.

Willem de Bruijn Dec. 22, 2020, 10:36 p.m. UTC | #3

On Tue, Dec 22, 2020 at 12:19 PM Jonathan Lemon
<[e-mail]> wrote:
>
> On Tue, Dec 22, 2020 at 09:42:40AM -0500, Willem de Bruijn wrote:
> > On Mon, Dec 21, 2020 at 7:09 PM Jonathan Lemon <[e-mail]> wrote:
> > >
> > > From: Jonathan Lemon <[e-mail]>
> > >
> > > Replace sock_zerocopy_put with the generic skb_zcopy_put()
> > > function.  Pass 'true' as the success argument, as this
> > > is identical to no change.
> > >
> > > Signed-off-by: Jonathan Lemon <[e-mail]>
> >
> > uarg->zerocopy may be false if sock_zerocopy_put_abort is called from
> > tcp_sendmsg_locked
>
> Yes, it may well be false.  The original logic goes:
>
>    sock_zerocopy_put_abort()
>    sock_zerocopy_put()
>    sock_zerocopy_callback(..., success = uarg->zerocopy)
>      if (success)
>
> The new logic is now:
>
>    sock_zerocopy_put_abort()
>    sock_zerocopy_callback(..., success = true)
>      uarg->zerocopy = uarg->zerocopy & success
>      if (uarg->zerocopy)
>
> The success value ls latched into uarg->zerocopy, and any failure
> is persistent.

Good point.

It's not entirely obvious, and a bit unintuitive to pass success in an
abort statement. But it works.

Abort does not schedule a notification if no skb associated with the
uarg was sent. And if it was, the zerocopy state will reflect the & of
all those packets. On which note, if renaming the currently
inconsistent name, maybe renaming to zerocopy_success is the more
descriptive one, then.

Patch

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index c9d7de9d624d..238166b522f7 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -499,7 +499,6 @@  static inline void sock_zerocopy_get(struct ubuf_info *uarg)
 	refcount_inc(&uarg->refcnt);
 }
 
-void sock_zerocopy_put(struct ubuf_info *uarg);
 void sock_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref);
 
 void sock_zerocopy_callback(struct ubuf_info *uarg, bool success);
@@ -1474,6 +1473,12 @@  static inline void *skb_zcopy_get_nouarg(struct sk_buff *skb)
 	return (void *)((uintptr_t) skb_shinfo(skb)->destructor_arg & ~0x1UL);
 }
 
+static inline void skb_zcopy_put(struct ubuf_info *uarg)
+{
+	if (uarg)
+		uarg->callback(uarg, true);
+}
+
 /* Release a reference on a zerocopy structure */
 static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
 {
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 73699dbdc4a1..984760dd670b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1251,13 +1251,6 @@  void sock_zerocopy_callback(struct ubuf_info *uarg, bool success)
 }
 EXPORT_SYMBOL_GPL(sock_zerocopy_callback);
 
-void sock_zerocopy_put(struct ubuf_info *uarg)
-{
-	if (uarg)
-		uarg->callback(uarg, uarg->zerocopy);
-}
-EXPORT_SYMBOL_GPL(sock_zerocopy_put);
-
 void sock_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
 {
 	if (uarg) {
@@ -1267,7 +1260,7 @@  void sock_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
 		uarg->len--;
 
 		if (have_uref)
-			sock_zerocopy_put(uarg);
+			skb_zcopy_put(uarg);
 	}
 }
 EXPORT_SYMBOL_GPL(sock_zerocopy_put_abort);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index fea9bae370e4..5c38080df13f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1429,7 +1429,7 @@  int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
 	}
 out_nopush:
-	sock_zerocopy_put(uarg);
+	skb_zcopy_put(uarg);
 	return copied + copied_syn;
 
 do_error: