# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1238497253 -3600
# Node ID 3a4410c4504ea64f2c1e873df3234938366050ad
# Parent ab1d4fbbe4bf93f203e0c4d62c18bd248e4f1d4a
sfc_netfront: Only clear tx_skb when ready for netif_wake_queue
(doing otherwise could result in a lost packet) and document use of
locks to protect tx_skb
Signed-off-by: Kieran Mansley <kmansley@xxxxxxxxxxxxxx>
---
drivers/xen/sfc_netfront/accel.h | 6 +++--
drivers/xen/sfc_netfront/accel_netfront.c | 4 +--
drivers/xen/sfc_netfront/accel_vi.c | 35 ++++++++++++------------------
3 files changed, 21 insertions(+), 24 deletions(-)
diff -r ab1d4fbbe4bf -r 3a4410c4504e drivers/xen/sfc_netfront/accel.h
--- a/drivers/xen/sfc_netfront/accel.h Tue Mar 31 12:00:03 2009 +0100
+++ b/drivers/xen/sfc_netfront/accel.h Tue Mar 31 12:00:53 2009 +0100
@@ -277,8 +277,10 @@ typedef struct netfront_accel_vnic {
int poll_enabled;
- /** A spare slot for a TX packet. This is treated as an extension
- * of the DMA queue. */
+ /** A spare slot for a TX packet. This is treated as an
+ * extension of the DMA queue. Reads require either
+ * netfront's tx_lock or the vnic tx_lock; writes require both
+ * locks */
struct sk_buff *tx_skb;
/** Keep track of fragments of SSR packets */
diff -r ab1d4fbbe4bf -r 3a4410c4504e drivers/xen/sfc_netfront/accel_netfront.c
--- a/drivers/xen/sfc_netfront/accel_netfront.c Tue Mar 31 12:00:03 2009 +0100
+++ b/drivers/xen/sfc_netfront/accel_netfront.c Tue Mar 31 12:00:53 2009 +0100
@@ -65,7 +65,7 @@ static int netfront_accel_netdev_start_x
BUG_ON(vnic->net_dev != net_dev);
DPRINTK("%s stopping queue\n", __FUNCTION__);
- /* Netfront's lock protects tx_skb */
+ /* Need netfront's tx_lock and vnic tx_lock to write tx_skb */
spin_lock_irqsave(&np->tx_lock, flags2);
BUG_ON(vnic->tx_skb != NULL);
vnic->tx_skb = skb;
@@ -183,7 +183,7 @@ static int netfront_accel_check_ready(st
BUG_ON(vnic == NULL);
- /* This is protected by netfront's lock */
+ /* Read of tx_skb is protected by netfront's tx_lock */
return vnic->tx_skb == NULL;
}
diff -r ab1d4fbbe4bf -r 3a4410c4504e drivers/xen/sfc_netfront/accel_vi.c
--- a/drivers/xen/sfc_netfront/accel_vi.c Tue Mar 31 12:00:03 2009 +0100
+++ b/drivers/xen/sfc_netfront/accel_vi.c Tue Mar 31 12:00:53 2009 +0100
@@ -991,39 +991,35 @@ static void netfront_accel_vi_not_busy(n
{
struct netfront_info *np = ((struct netfront_info *)
netdev_priv(vnic->net_dev));
- struct sk_buff *skb;
int handled;
unsigned long flags;
-
+
/*
- * TODO if we could safely check tx_skb == NULL and return
- * early without taking the lock, that would obviously help
- * performance
- */
-
- /* Take the netfront lock which protects tx_skb. */
- spin_lock_irqsave(&np->tx_lock, flags);
+ * We hold the vnic tx_lock which is sufficient to exclude
+ * writes to tx_skb
+ */
+
if (vnic->tx_skb != NULL) {
DPRINTK("%s trying to send spare buffer\n", __FUNCTION__);
- skb = vnic->tx_skb;
- vnic->tx_skb = NULL;
-
- spin_unlock_irqrestore(&np->tx_lock, flags);
-
- handled = netfront_accel_vi_tx_post(vnic, skb);
+ handled = netfront_accel_vi_tx_post(vnic, vnic->tx_skb);
- spin_lock_irqsave(&np->tx_lock, flags);
-
if (handled != NETFRONT_ACCEL_STATUS_BUSY) {
DPRINTK("%s restarting tx\n", __FUNCTION__);
+
+ /* Need netfront tx_lock and vnic tx_lock to
+ * write tx_skb */
+ spin_lock_irqsave(&np->tx_lock, flags);
+
+ vnic->tx_skb = NULL;
+
if (netfront_check_queue_ready(vnic->net_dev)) {
netif_wake_queue(vnic->net_dev);
NETFRONT_ACCEL_STATS_OP
(vnic->stats.queue_wakes++);
}
- } else {
- vnic->tx_skb = skb;
+ spin_unlock_irqrestore(&np->tx_lock, flags);
+
}
/*
@@ -1032,7 +1028,6 @@ static void netfront_accel_vi_not_busy(n
*/
BUG_ON(handled == NETFRONT_ACCEL_STATUS_CANT);
}
- spin_unlock_irqrestore(&np->tx_lock, flags);
}
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