On Wed, Oct 14, 2026 at 07:56:39PM +0800, Jia Jia wrote:
>Each received packet updates peer credit and may call sk_write_space().
>A writer cannot use that credit until the batch releases the socket lock,
>so one notification at batch finish is sufficient.
>
>Save the initial sk_write_space callback when the AF_VSOCK socket is
>created and require it to remain installed for batching. This lets the
>transport module deliver the deferred notification without referring to
>the unexported default callback. Sockets with replaced callbacks retain
>their per-packet behavior.
>
>Record the batch socket before processing its first packet so a batch that
>ends on that packet cannot lose the pending notification.
mmm, is this a fix of the previous patch?
No. Patch 2 preserves the existing per-packet sk_write_space()
behavior, so Patch 3 is not a correctness fix for it. Patch 3 only
coalesces the native/ default notifications.
Moving batch->sk earlier is required only after the deferred state is
introduced here: the socket must already be recorded before the first
packet can set write_space_pending, so the notification can still be
delivered if that packet immediately ends the batch. Sorry, the commit
message did not make this distinction clear.
>
>Signed-off-by: Jia Jia <[email protected]>
>---
> include/linux/virtio_vsock.h | 1 +
> include/net/af_vsock.h | 5 +++
> net/vmw_vsock/af_vsock.c | 1 +
> net/vmw_vsock/virtio_transport_common.c | 53 +++++++++++++++++--------
> 4 files changed, 44 insertions(+), 16 deletions(-)
>
>diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>index 26dde6909c4ed..bf077ee0ded88 100644
>--- a/include/linux/virtio_vsock.h
>+++ b/include/linux/virtio_vsock.h
>@@ -287,6 +287,7 @@ struct virtio_transport_rx_batch {
> struct sock *sk;
> unsigned int pkts;
> size_t bytes;
>+ bool write_space_pending;
> };
>
> void virtio_transport_recv_pkt_batch(struct virtio_transport *t,
>diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>index 5549298c1ec6b..9a40960d10cbe 100644
>--- a/include/net/af_vsock.h
>+++ b/include/net/af_vsock.h
>@@ -63,6 +63,11 @@ struct vsock_sock {
> u32 peer_shutdown;
> bool sent_request;
> bool ignore_connecting_rst;
>+ /*
>+ * Initial callback, used to identify replacements and deliver deferred
>+ * write-space notifications.
>+ */
>+ void (*default_write_space)(struct sock *sk);
This is kind of virtio-vsock specific, why need to be here?
I stored this state here because __vsock_create() can capture the
native callback before the socket is exposed or any callback
replacement occurs, and the transport cannot directly reference the
unexported default callback. However, I agree that exposing this
virtio-specific state directly in struct vsock_sock is not ideal. I'll
look at hiding it behind an AF_VSOCK helper in v5 while preserving the
capture point and the lifetime required by deferred callbacks.
>
> /* Protected by lock_sock(sk) */
> u64 buffer_size;
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index 44cee74519555..fe7f49da6c4bc 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -958,6 +958,7 @@ static struct sock *__vsock_create(struct net *net,
> sk->sk_type = type;
>
> vsk = vsock_sk(sk);
>+ vsk->default_write_space = sk->sk_write_space;
> vsock_addr_init(&vsk->local_addr, VMADDR_CID_ANY, VMADDR_PORT_ANY);
> vsock_addr_init(&vsk->remote_addr, VMADDR_CID_ANY, VMADDR_PORT_ANY);
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c
b/net/vmw_vsock/virtio_transport_common.c
>index ff74e805527a5..f4b5f0230493e 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -1820,6 +1820,7 @@ virtio_transport_recv_pkt_batchable(struct
virtio_transport *t,
> return sk->sk_state == TCP_ESTABLISHED &&
> sk->sk_type == SOCK_STREAM &&
> READ_ONCE(sk->sk_prot) == sk->sk_prot_creator &&
>+ READ_ONCE(sk->sk_write_space) == vsk->default_write_space &&
Why?
I believe this check is necessary because notification coalescing is
only safe for the original native sk_write_space callback. Sockmap can
replace this callback under sk_callback_lock, which is independent of
the socket lock held across the batch, and the replacement may require
per-packet handling. Comparing it with the callback captured at socket
creation lets us fall back to the existing per-packet behavior when it
has been replaced. I'll add a comment explaining this.
> !sock_flag(sk, SOCK_DONE) &&
> vsk->transport == &t->transport &&
> vvs && virtio_transport_rx_skb_has_headroom(vvs) &&
>@@ -1828,13 +1829,15 @@ virtio_transport_recv_pkt_batchable(struct
virtio_transport *t,
>
> /*
> * The caller holds sk's socket lock. Set @batchable if the socket can remain
>- * locked for another ordinary STREAM/RW packet. Return true if the caller
>- * must free @skb.
>+ * locked for another ordinary STREAM/RW packet. When @batch is non-NULL,
>+ * record a default write-space notification for batch finish instead of
>+ * delivering it immediately. Return true if the caller must free @skb.
> */
> static bool
> virtio_transport_recv_pkt_locked(struct virtio_transport *t,
> struct sk_buff *skb, struct sock *sk,
>- bool *batchable)
>+ bool *batchable,
>+ struct virtio_transport_rx_batch *batch)
> {
> struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
> struct sockaddr_vm src;
>@@ -1863,8 +1866,12 @@ virtio_transport_recv_pkt_locked(struct
virtio_transport *t,
> if (vsk->local_addr.svm_cid != VMADDR_CID_ANY)
> vsk->local_addr.svm_cid = le64_to_cpu(hdr->dst_cid);
>
>- if (space_available)
>- sk->sk_write_space(sk);
>+ if (space_available) {
>+ if (batch)
>+ batch->write_space_pending = true;
>+ else
>+ sk->sk_write_space(sk);
>+ }
>
> switch (sk->sk_state) {
> case TCP_LISTEN:
>@@ -1931,7 +1938,7 @@ void virtio_transport_recv_pkt(struct virtio_transport
*t,
> }
>
> lock_sock(sk);
>- free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk, NULL);
>+ free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk, NULL, NULL);
> release_sock(sk);
>
> /* Release refcnt obtained when we fetched this socket out of the
>@@ -1949,22 +1956,27 @@ EXPORT_SYMBOL_GPL(virtio_transport_recv_pkt);
>
> /*
> * Finish the RX batch.
>- * For a non-empty batch, the caller must hold the socket lock acquired with
>- * lock_sock(). This function releases the lock and the batch's lookup
>- * reference.
>+ * For a non-empty batch, the caller holds the socket lock acquired with
>+ * lock_sock(). Deliver any deferred write-space notification while the lock
>+ * is held, then release the lock and the batch's lookup reference.
> * An empty batch is a no-op.
> */
> void virtio_transport_rx_batch_finish(struct virtio_transport_rx_batch *batch)
> {
>+ bool write_space_pending = batch->write_space_pending;
> struct sock *sk = batch->sk;
>
> batch->sk = NULL;
> batch->pkts = 0;
> batch->bytes = 0;
>+ batch->write_space_pending = false;
>
> if (!sk)
> return;
>
>+ if (write_space_pending)
>+ vsock_sk(sk)->default_write_space(sk);
>+
> release_sock(sk);
> sock_put(sk);
> }
>@@ -2019,7 +2031,8 @@ void virtio_transport_recv_pkt_batch(struct
virtio_transport *t,
> }
>
> free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk,
>- &batchable);
>+ &batchable,
>+ batch);
> if (!batchable)
> virtio_transport_rx_batch_finish(batch);
> if (free_pkt)
>@@ -2059,23 +2072,31 @@ void virtio_transport_recv_pkt_batch(struct
virtio_transport *t,
>
> lock_sock(sk);
> /*
>- * Sockmap removal restores the native protocol under sk_callback_lock.
>- * Serialize this initial eligibility check with that update.
>+ * Sockmap teardown restores callbacks under sk_callback_lock. Keep the
>+ * initial eligibility check consistent with that update.
> */
Unrelated change?
This is related to the new callback eligibility check, but I agree
that the original rewrite was unnecessary. I’ll keep the original
serialization wording and only extend the comment to mention both the
native protocol and callbacks.
BTW if you are assisted by AI, please read
https://docs.kernel.org/process/coding-assistants.html
Thanks for the reminder. I read the document when you mentioned it
previously. take responsibility for every change in it. As this
review has shown, I missed some netdev conventions, and the patch
organization can also be improved; those are my mistakes, and I’ll
address them in v5.
I used an LLM to help set up the test environment, translate and
polish the English text, and review the series. I ran and verified the
tests myself. I’ll
disclose that assistance in v5 as described in the documentation.
