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Date:	Fri, 8 Aug 2014 17:37:12 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	<netdev@...r.kernel.org>, <xen-devel@...ts.xen.org>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Zoltan Kiss <zoltan.kiss@...rix.com>
Subject: [PATCH net v2 2/3] xen-netback: don't stop dealloc kthread too early

Reference count the number of packets in host stack, so that we don't
stop the deallocation thread too early. If not, we can end up with
xenvif_free permanently waiting for deallocation thread to unmap grefs.

Reported-by: Thomas Leonard <talex5@...il.com>
Signed-off-by: Wei Liu <wei.liu2@...rix.com>
Cc: Ian Campbell <ian.campbell@...rix.com>
Cc: Zoltan Kiss <zoltan.kiss@...rix.com>
---
 drivers/net/xen-netback/common.h    |    5 +++++
 drivers/net/xen-netback/interface.c |   16 ++++++++++++++++
 drivers/net/xen-netback/netback.c   |   24 ++++++++++++++++++++----
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index ef3026f..d9b7f85 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -165,6 +165,8 @@ struct xenvif_queue { /* Per-queue data for xenvif */
 	u16 dealloc_ring[MAX_PENDING_REQS];
 	struct task_struct *dealloc_task;
 	wait_queue_head_t dealloc_wq;
+	wait_queue_head_t inflight_wq;
+	atomic_t inflight_packets;
 
 	/* Use kthread for guest RX */
 	struct task_struct *task;
@@ -329,4 +331,7 @@ extern unsigned int xenvif_max_queues;
 extern struct dentry *xen_netback_dbg_root;
 #endif
 
+void xenvif_inc_inflight_packets(struct xenvif_queue *queue);
+void xenvif_dec_inflight_packets(struct xenvif_queue *queue);
+
 #endif /* __XEN_NETBACK__COMMON_H__ */
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index fdb4fca..6488801 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -43,6 +43,17 @@
 #define XENVIF_QUEUE_LENGTH 32
 #define XENVIF_NAPI_WEIGHT  64
 
+void xenvif_inc_inflight_packets(struct xenvif_queue *queue)
+{
+	atomic_inc(&queue->inflight_packets);
+}
+
+void xenvif_dec_inflight_packets(struct xenvif_queue *queue)
+{
+	if (atomic_dec_and_test(&queue->inflight_packets))
+		wake_up(&queue->inflight_wq);
+}
+
 static inline void xenvif_stop_queue(struct xenvif_queue *queue)
 {
 	struct net_device *dev = queue->vif->dev;
@@ -561,6 +572,8 @@ int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
 
 	init_waitqueue_head(&queue->wq);
 	init_waitqueue_head(&queue->dealloc_wq);
+	init_waitqueue_head(&queue->inflight_wq);
+	atomic_set(&queue->inflight_packets, 0);
 
 	if (tx_evtchn == rx_evtchn) {
 		/* feature-split-event-channels == 0 */
@@ -687,6 +700,9 @@ void xenvif_disconnect(struct xenvif *vif)
 			queue->task = NULL;
 		}
 
+		wait_event(queue->inflight_wq,
+			   atomic_read(&queue->inflight_packets) == 0);
+
 		if (queue->dealloc_task) {
 			kthread_stop(queue->dealloc_task);
 			queue->dealloc_task = NULL;
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 4734472..d2f0c7d7 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -107,6 +107,18 @@ static inline unsigned long idx_to_kaddr(struct xenvif_queue *queue,
 #define callback_param(vif, pending_idx) \
 	(vif->pending_tx_info[pending_idx].callback_struct)
 
+/* This function is used to set SKBTX_DEV_ZEROCOPY as well as
+ * increasing the inflight counter. We need to increase the inflight
+ * counter because core driver calls into xenvif_zerocopy_callback
+ * which calls xenvif_dec_inflight_packets.
+ */
+static void set_skb_zerocopy(struct xenvif_queue *queue,
+			     struct sk_buff *skb)
+{
+	skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+	xenvif_inc_inflight_packets(queue);
+}
+
 /* Find the containing VIF's structure from a pointer in pending_tx_info array
  */
 static inline struct xenvif_queue *ubuf_to_queue(const struct ubuf_info *ubuf)
@@ -1525,10 +1537,13 @@ static int xenvif_handle_frag_list(struct xenvif_queue *queue, struct sk_buff *s
 	/* remove traces of mapped pages and frag_list */
 	skb_frag_list_init(skb);
 	uarg = skb_shinfo(skb)->destructor_arg;
+	/* See comment on set_skb_zerocopy */
+	if (uarg->callback == xenvif_zerocopy_callback)
+		xenvif_inc_inflight_packets(queue);
 	uarg->callback(uarg, true);
 	skb_shinfo(skb)->destructor_arg = NULL;
 
-	skb_shinfo(nskb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+	set_skb_zerocopy(queue, nskb);
 	kfree_skb(nskb);
 
 	return 0;
@@ -1589,7 +1604,7 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
 				if (net_ratelimit())
 					netdev_err(queue->vif->dev,
 						   "Not enough memory to consolidate frag_list!\n");
-				skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+				set_skb_zerocopy(queue, skb);
 				kfree_skb(skb);
 				continue;
 			}
@@ -1609,7 +1624,7 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
 				   "Can't setup checksum in net_tx_action\n");
 			/* We have to set this flag to trigger the callback */
 			if (skb_shinfo(skb)->destructor_arg)
-				skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+				set_skb_zerocopy(queue, skb);
 			kfree_skb(skb);
 			continue;
 		}
@@ -1641,7 +1656,7 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
 		 * skb. E.g. the __pskb_pull_tail earlier can do such thing.
 		 */
 		if (skb_shinfo(skb)->destructor_arg) {
-			skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+			set_skb_zerocopy(queue, skb);
 			queue->stats.tx_zerocopy_sent++;
 		}
 
@@ -1681,6 +1696,7 @@ void xenvif_zerocopy_callback(struct ubuf_info *ubuf, bool zerocopy_success)
 		queue->stats.tx_zerocopy_success++;
 	else
 		queue->stats.tx_zerocopy_fail++;
+	xenvif_dec_inflight_packets(queue);
 }
 
 static inline void xenvif_tx_dealloc_action(struct xenvif_queue *queue)
-- 
1.7.10.4

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