Re: [PATCH net-next v4 4/4] vsock/virtio: defer RX notifications until batch unlock

[Stefano Garzarella <sgarzare@redhat.com>]

On Wed, Oct 14, 2026 at 07:56:40PM +0800, Jia Jia wrote:
>An RX batch can make a socket readable while the worker still holds its
>socket lock. Waking a blocking reader then only moves it to waiting for
>the same lock.
>
>Record the existing low-watermark condition and notify once after
>release_sock(). Move the coalesced write-space notification after the
>unlock as well, since both callbacks wake sk_sleep(sk). Deliver
>write-space before data-ready and keep the lookup reference until both
>callbacks complete.
>
>As with write-space, save the initial sk_data_ready callback and batch only
>while both saved callbacks remain installed. Sockets with replaced
>callbacks retain their per-packet behavior.
>
>The existing psock-marker check also covers a concurrent sockmap attach:
>at most the already admitted packet completes on the native path, and the
>next packet ends the batch.
>
>Signed-off-by: Jia Jia <physicalmtea@gmail.com>
>---
> 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 | 35 ++++++++++++++++++-------
> 4 files changed, 31 insertions(+), 11 deletions(-)
>
>diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>index bf077ee0ded88..f1396ca3ad9b5 100644
>--- a/include/linux/virtio_vsock.h
>+++ b/include/linux/virtio_vsock.h
>@@ -288,6 +288,7 @@ struct virtio_transport_rx_batch {
> 	unsigned int pkts;
> 	size_t bytes;
> 	bool write_space_pending;
>+	bool data_ready_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 9a40960d10cbe..78bab5820f528 100644
>--- a/include/net/af_vsock.h
>+++ b/include/net/af_vsock.h
>@@ -64,9 +64,10 @@ struct vsock_sock {
> 	bool sent_request;
> 	bool ignore_connecting_rst;
> 	/*
>-	 * Initial callback, used to identify replacements and deliver deferred
>-	 * write-space notifications.
>+	 * Initial callbacks, used to identify replacements and deliver deferred
>+	 * notifications.
> 	 */
>+	void (*default_data_ready)(struct sock *sk);
> 	void (*default_write_space)(struct sock *sk);
>
> 	/* Protected by lock_sock(sk) */
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index fe7f49da6c4bc..f40659ec29df0 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_data_ready = sk->sk_data_ready;
> 	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 f4b5f0230493e..8b62b789b71c5 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -1588,7 +1588,8 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
>
> static int
> virtio_transport_recv_connected(struct sock *sk,
>-				struct sk_buff *skb)
>+				struct sk_buff *skb,
>+				bool *data_ready_pending)
> {
> 	struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
> 	struct vsock_sock *vsk = vsock_sk(sk);
>@@ -1607,7 +1608,13 @@ virtio_transport_recv_connected(struct sock *sk,
> 			vsock_remove_sock(vsk);
> 			break;
> 		}
>-		vsock_data_ready(sk);
>+		if (!data_ready_pending) {
>+			vsock_data_ready(sk);
>+		} else if (!*data_ready_pending &&
>+			   (vsock_stream_has_data(vsk) >= sk->sk_rcvlowat ||
>+			    sock_flag(sk, SOCK_DONE))) {
>+			*data_ready_pending = true;
>+		}
> 		return err;
> 	case VIRTIO_VSOCK_OP_CREDIT_REQUEST:
> 		virtio_transport_send_credit_update(vsk);
>@@ -1820,6 +1827,7 @@ 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_data_ready) == vsk->default_data_ready &&
> 	       READ_ONCE(sk->sk_write_space) == vsk->default_write_space &&
> 	       !sock_flag(sk, SOCK_DONE) &&
> 	       vsk->transport == &t->transport &&
>@@ -1830,8 +1838,9 @@ 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.  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.
>+ * record default write-space and data-ready notifications for batch finish
>+ * instead of delivering them immediately.  Return true if the caller must
>+ * free @skb.
>  */
> static bool
> virtio_transport_recv_pkt_locked(struct virtio_transport *t,
>@@ -1883,7 +1892,9 @@ virtio_transport_recv_pkt_locked(struct virtio_transport *t,
> 		kfree_skb(skb);
> 		break;
> 	case TCP_ESTABLISHED:
>-		virtio_transport_recv_connected(sk, skb);
>+		virtio_transport_recv_connected(sk, skb,
>+						batch ?
>+						&batch->data_ready_pending : NULL);
> 		break;
> 	case TCP_CLOSING:
> 		virtio_transport_recv_disconnecting(sk, skb);
>@@ -1957,27 +1968,33 @@ EXPORT_SYMBOL_GPL(virtio_transport_recv_pkt);
> /*
>  * Finish the RX batch.
>  * 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.
>+ * lock_sock(). Release the lock, deliver any deferred write-space and
>+ * data-ready notifications in that order, then drop 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;
>+	bool data_ready_pending = batch->data_ready_pending;
> 	struct sock *sk = batch->sk;
>
> 	batch->sk = NULL;
> 	batch->pkts = 0;
> 	batch->bytes = 0;
> 	batch->write_space_pending = false;
>+	batch->data_ready_pending = false;
>
> 	if (!sk)
> 		return;
>
>+	release_sock(sk);
>+

Why in the previous patch we release the socket after calling 
default_write_space() and now we are moving before?

> 	if (write_space_pending)
> 		vsock_sk(sk)->default_write_space(sk);
>
>-	release_sock(sk);
>+	if (data_ready_pending)
>+		vsock_sk(sk)->default_data_ready(sk);
>+
> 	sock_put(sk);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_rx_batch_finish);
>-- 
>2.53.0
>