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Subject[PATCH v3 2/5] net: qrtr: Implement outgoing flow control
Date
In order to prevent overconsumption of resources on the remote side QRTR
implements a flow control mechanism.

The mechanism works by the sender keeping track of the number of
outstanding unconfirmed messages that has been transmitted to a
particular node/port pair.

Upon count reaching a low watermark (L) the confirm_rx bit is set in the
outgoing message and when the count reaching a high watermark (H)
transmission will be blocked upon the reception of a resume_tx message
from the remote, that resets the counter to 0.

This guarantees that there will be at most 2H - L messages in flight.
Values chosen for L and H are 5 and 10 respectively.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---

Changes since v2:
- Replaced atomic "pending" with in and the use of a spin_lockon &resume_tx.lock
- Move wait queue into qrtr_tx_flow struct to only wake up the sleepers that
are actually affected by the notification
- Take spinlock around the check in qrtr_tx_wait(), so that we don't need to
spin around the wait_event to prevent > H clients continuing

net/qrtr/qrtr.c | 189 ++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 182 insertions(+), 7 deletions(-)

diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
index 6c56a8ce83ef..a6da5fa2a9b5 100644
--- a/net/qrtr/qrtr.c
+++ b/net/qrtr/qrtr.c
@@ -8,6 +8,7 @@
#include <linux/qrtr.h>
#include <linux/termios.h> /* For TIOCINQ/OUTQ */
#include <linux/numa.h>
+#include <linux/wait.h>

#include <net/sock.h>

@@ -113,6 +114,8 @@ static DEFINE_MUTEX(qrtr_port_lock);
* @ep: endpoint
* @ref: reference count for node
* @nid: node id
+ * @qrtr_tx_flow: tree of qrtr_tx_flow, keyed by node << 32 | port
+ * @qrtr_tx_lock: lock for qrtr_tx_flow inserts
* @rx_queue: receive queue
* @work: scheduled work struct for recv work
* @item: list item for broadcast list
@@ -123,11 +126,29 @@ struct qrtr_node {
struct kref ref;
unsigned int nid;

+ struct radix_tree_root qrtr_tx_flow;
+ struct mutex qrtr_tx_lock; /* for qrtr_tx_flow */
+
struct sk_buff_head rx_queue;
struct work_struct work;
struct list_head item;
};

+/**
+ * struct qrtr_tx_flow - tx flow control
+ * @resume_tx: waiters for a resume tx from the remote
+ * @pending: number of waiting senders
+ * @tx_failed: indicates that a message with confirm_rx flag was lost
+ */
+struct qrtr_tx_flow {
+ struct wait_queue_head resume_tx;
+ int pending;
+ int tx_failed;
+};
+
+#define QRTR_TX_FLOW_HIGH 10
+#define QRTR_TX_FLOW_LOW 5
+
static int qrtr_local_enqueue(struct qrtr_node *node, struct sk_buff *skb,
int type, struct sockaddr_qrtr *from,
struct sockaddr_qrtr *to);
@@ -142,7 +163,9 @@ static int qrtr_bcast_enqueue(struct qrtr_node *node, struct sk_buff *skb,
*/
static void __qrtr_node_release(struct kref *kref)
{
+ struct radix_tree_iter iter;
struct qrtr_node *node = container_of(kref, struct qrtr_node, ref);
+ void __rcu **slot;

if (node->nid != QRTR_EP_NID_AUTO)
radix_tree_delete(&qrtr_nodes, node->nid);
@@ -152,6 +175,12 @@ static void __qrtr_node_release(struct kref *kref)

cancel_work_sync(&node->work);
skb_queue_purge(&node->rx_queue);
+
+ /* Free tx flow counters */
+ radix_tree_for_each_slot(slot, &node->qrtr_tx_flow, &iter, 0) {
+ radix_tree_iter_delete(&node->qrtr_tx_flow, &iter, slot);
+ kfree(*slot);
+ }
kfree(node);
}

@@ -171,6 +200,122 @@ static void qrtr_node_release(struct qrtr_node *node)
kref_put_mutex(&node->ref, __qrtr_node_release, &qrtr_node_lock);
}

+/**
+ * qrtr_tx_resume() - reset flow control counter
+ * @node: qrtr_node that the QRTR_TYPE_RESUME_TX packet arrived on
+ * @skb: resume_tx packet
+ */
+static void qrtr_tx_resume(struct qrtr_node *node, struct sk_buff *skb)
+{
+ struct qrtr_ctrl_pkt *pkt = (struct qrtr_ctrl_pkt *)skb->data;
+ u64 remote_node = le32_to_cpu(pkt->client.node);
+ u32 remote_port = le32_to_cpu(pkt->client.port);
+ struct qrtr_tx_flow *flow;
+ unsigned long key;
+
+ key = remote_node << 32 | remote_port;
+
+ flow = radix_tree_lookup(&node->qrtr_tx_flow, key);
+ if (flow) {
+ spin_lock(&flow->resume_tx.lock);
+ flow->pending = 0;
+ spin_unlock(&flow->resume_tx.lock);
+ wake_up_interruptible_all(&flow->resume_tx);
+ }
+
+ consume_skb(skb);
+}
+
+/**
+ * qrtr_tx_wait() - flow control for outgoing packets
+ * @node: qrtr_node that the packet is to be send to
+ * @dest_node: node id of the destination
+ * @dest_port: port number of the destination
+ * @type: type of message
+ *
+ * The flow control scheme is based around the low and high "watermarks". When
+ * the low watermark is passed the confirm_rx flag is set on the outgoing
+ * message, which will trigger the remote to send a control message of the type
+ * QRTR_TYPE_RESUME_TX to reset the counter. If the high watermark is hit
+ * further transmision should be paused.
+ *
+ * Return: 1 if confirm_rx should be set, 0 otherwise or errno failure
+ */
+static int qrtr_tx_wait(struct qrtr_node *node, int dest_node, int dest_port,
+ int type)
+{
+ unsigned long key = (u64)dest_node << 32 | dest_port;
+ struct qrtr_tx_flow *flow;
+ int confirm_rx = 0;
+ int ret;
+
+ /* Never set confirm_rx on non-data packets */
+ if (type != QRTR_TYPE_DATA)
+ return 0;
+
+ mutex_lock(&node->qrtr_tx_lock);
+ flow = radix_tree_lookup(&node->qrtr_tx_flow, key);
+ if (!flow) {
+ flow = kzalloc(sizeof(*flow), GFP_KERNEL);
+ if (flow) {
+ init_waitqueue_head(&flow->resume_tx);
+ radix_tree_insert(&node->qrtr_tx_flow, key, flow);
+ }
+ }
+ mutex_unlock(&node->qrtr_tx_lock);
+
+ /* Set confirm_rx if we where unable to find and allocate a flow */
+ if (!flow)
+ return 1;
+
+ spin_lock_irq(&flow->resume_tx.lock);
+ ret = wait_event_interruptible_locked_irq(flow->resume_tx,
+ flow->pending < QRTR_TX_FLOW_HIGH ||
+ flow->tx_failed ||
+ !node->ep);
+ if (ret < 0) {
+ confirm_rx = ret;
+ } else if (!node->ep) {
+ confirm_rx = -EPIPE;
+ } else if (flow->tx_failed) {
+ flow->tx_failed = 0;
+ confirm_rx = 1;
+ } else {
+ flow->pending++;
+ confirm_rx = flow->pending == QRTR_TX_FLOW_LOW;
+ }
+ spin_unlock_irq(&flow->resume_tx.lock);
+
+ return confirm_rx;
+}
+
+/**
+ * qrtr_tx_flow_failed() - flag that tx of confirm_rx flagged messages failed
+ * @node: qrtr_node that the packet is to be send to
+ * @dest_node: node id of the destination
+ * @dest_port: port number of the destination
+ *
+ * Signal that the transmission of a message with confirm_rx flag failed. The
+ * flow's "pending" counter will keep incrementing towards QRTR_TX_FLOW_HIGH,
+ * at which point transmission would stall forever waiting for the resume TX
+ * message associated with the dropped confirm_rx message.
+ * Work around this by marking the flow as having a failed transmission and
+ * cause the next transmission attempt to be sent with the confirm_rx.
+ */
+static void qrtr_tx_flow_failed(struct qrtr_node *node, int dest_node,
+ int dest_port)
+{
+ unsigned long key = (u64)dest_node << 32 | dest_port;
+ struct qrtr_tx_flow *flow;
+
+ flow = radix_tree_lookup(&node->qrtr_tx_flow, key);
+ if (flow) {
+ spin_lock_irq(&flow->resume_tx.lock);
+ flow->tx_failed = 1;
+ spin_unlock_irq(&flow->resume_tx.lock);
+ }
+}
+
/* Pass an outgoing packet socket buffer to the endpoint driver. */
static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
int type, struct sockaddr_qrtr *from,
@@ -179,6 +324,13 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
struct qrtr_hdr_v1 *hdr;
size_t len = skb->len;
int rc = -ENODEV;
+ int confirm_rx;
+
+ confirm_rx = qrtr_tx_wait(node, to->sq_node, to->sq_port, type);
+ if (confirm_rx < 0) {
+ kfree_skb(skb);
+ return confirm_rx;
+ }

hdr = skb_push(skb, sizeof(*hdr));
hdr->version = cpu_to_le32(QRTR_PROTO_VER_1);
@@ -194,7 +346,7 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
}

hdr->size = cpu_to_le32(len);
- hdr->confirm_rx = 0;
+ hdr->confirm_rx = !!confirm_rx;

skb_put_padto(skb, ALIGN(len, 4));

@@ -205,6 +357,11 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
kfree_skb(skb);
mutex_unlock(&node->ep_lock);

+ /* Need to ensure that a subsequent message carries the otherwise lost
+ * confirm_rx flag if we dropped this one */
+ if (rc && confirm_rx)
+ qrtr_tx_flow_failed(node, to->sq_node, to->sq_port);
+
return rc;
}

@@ -311,7 +468,8 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
if (len != ALIGN(size, 4) + hdrlen)
goto err;

- if (cb->dst_port != QRTR_PORT_CTRL && cb->type != QRTR_TYPE_DATA)
+ if (cb->dst_port != QRTR_PORT_CTRL && cb->type != QRTR_TYPE_DATA &&
+ cb->type != QRTR_TYPE_RESUME_TX)
goto err;

skb_put_data(skb, data + hdrlen, size);
@@ -370,14 +528,18 @@ static void qrtr_node_rx_work(struct work_struct *work)

qrtr_node_assign(node, cb->src_node);

- ipc = qrtr_port_lookup(cb->dst_port);
- if (!ipc) {
- kfree_skb(skb);
+ if (cb->type == QRTR_TYPE_RESUME_TX) {
+ qrtr_tx_resume(node, skb);
} else {
- if (sock_queue_rcv_skb(&ipc->sk, skb))
+ ipc = qrtr_port_lookup(cb->dst_port);
+ if (!ipc) {
kfree_skb(skb);
+ } else {
+ if (sock_queue_rcv_skb(&ipc->sk, skb))
+ kfree_skb(skb);

- qrtr_port_put(ipc);
+ qrtr_port_put(ipc);
+ }
}
}
}
@@ -408,6 +570,8 @@ int qrtr_endpoint_register(struct qrtr_endpoint *ep, unsigned int nid)
node->nid = QRTR_EP_NID_AUTO;
node->ep = ep;

+ INIT_RADIX_TREE(&node->qrtr_tx_flow, GFP_KERNEL);
+
qrtr_node_assign(node, nid);

mutex_lock(&qrtr_node_lock);
@@ -428,8 +592,11 @@ void qrtr_endpoint_unregister(struct qrtr_endpoint *ep)
struct qrtr_node *node = ep->node;
struct sockaddr_qrtr src = {AF_QIPCRTR, node->nid, QRTR_PORT_CTRL};
struct sockaddr_qrtr dst = {AF_QIPCRTR, qrtr_local_nid, QRTR_PORT_CTRL};
+ struct radix_tree_iter iter;
struct qrtr_ctrl_pkt *pkt;
+ struct qrtr_tx_flow *flow;
struct sk_buff *skb;
+ void __rcu **slot;

mutex_lock(&node->ep_lock);
node->ep = NULL;
@@ -442,6 +609,14 @@ void qrtr_endpoint_unregister(struct qrtr_endpoint *ep)
qrtr_local_enqueue(NULL, skb, QRTR_TYPE_BYE, &src, &dst);
}

+ /* Wake up any transmitters waiting for resume-tx from the node */
+ mutex_lock(&node->qrtr_tx_lock);
+ radix_tree_for_each_slot(slot, &node->qrtr_tx_flow, &iter, 0) {
+ flow = *slot;
+ wake_up_interruptible_all(&flow->resume_tx);
+ }
+ mutex_unlock(&node->qrtr_tx_lock);
+
qrtr_node_release(node);
ep->node = NULL;
}
--
2.24.0
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