[Xen-devel] [PATCH net v3 2/3] xen-netback: don't stop dealloc kthread too early

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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@xxxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
---
 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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