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Message-ID: <1391543677-24039-1-git-send-email-zoltan.kiss@citrix.com>
Date: Tue, 4 Feb 2014 19:54:37 +0000
From: Zoltan Kiss <zoltan.kiss@...rix.com>
To: <ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
CC: Zoltan Kiss <zoltan.kiss@...rix.com>
Subject: [PATCH net v3] xen-netback: Fix Rx stall due to race condition
The recent patch to fix receive side flow control
(11b57f90257c1d6a91cee720151b69e0c2020cf6: xen-netback: stop vif thread
spinning if frontend is unresponsive) solved the spinning thread problem,
however caused an another one. The receive side can stall, if:
- [THREAD] xenvif_rx_action sets rx_queue_stopped to true
- [INTERRUPT] interrupt happens, and sets rx_event to true
- [THREAD] then xenvif_kthread sets rx_event to false
- [THREAD] rx_work_todo doesn't return true anymore
Also, if interrupt sent but there is still no room in the ring, it take quite a
long time until xenvif_rx_action realize it. This patch ditch that two variable,
and rework rx_work_todo. If the thread finds it can't fit more skb's into the
ring, it saves the last slot estimation into rx_last_skb_slots, otherwise it's
kept as 0. Then rx_work_todo will check if:
- there is something to send to the ring (like before)
- there is space for the topmost packet in the queue
I think that's more natural and optimal thing to test than two bool which are
set somewhere else.
Signed-off-by: Zoltan Kiss <zoltan.kiss@...rix.com>
Reviewed-by: Paul Durrant <paul.durrant@...rix.com>
Acked-by: Wei Liu <wei.liu2@...rix.com>
---
v2:
- Improve description of the problem
v3:
- Change subject and resend against net to emphasize this is a bugfix
drivers/net/xen-netback/common.h | 6 +-----
drivers/net/xen-netback/interface.c | 1 -
drivers/net/xen-netback/netback.c | 16 ++++++----------
3 files changed, 7 insertions(+), 16 deletions(-)
diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 4c76bcb..ae413a2 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -143,11 +143,7 @@ struct xenvif {
char rx_irq_name[IFNAMSIZ+4]; /* DEVNAME-rx */
struct xen_netif_rx_back_ring rx;
struct sk_buff_head rx_queue;
- bool rx_queue_stopped;
- /* Set when the RX interrupt is triggered by the frontend.
- * The worker thread may need to wake the queue.
- */
- bool rx_event;
+ RING_IDX rx_last_skb_slots;
/* This array is allocated seperately as it is large */
struct gnttab_copy *grant_copy_op;
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index b9de31e..7669d49 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -100,7 +100,6 @@ static irqreturn_t xenvif_rx_interrupt(int irq, void *dev_id)
{
struct xenvif *vif = dev_id;
- vif->rx_event = true;
xenvif_kick_thread(vif);
return IRQ_HANDLED;
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 2738563..bb241d0 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -477,7 +477,6 @@ static void xenvif_rx_action(struct xenvif *vif)
unsigned long offset;
struct skb_cb_overlay *sco;
bool need_to_notify = false;
- bool ring_full = false;
struct netrx_pending_operations npo = {
.copy = vif->grant_copy_op,
@@ -487,7 +486,7 @@ static void xenvif_rx_action(struct xenvif *vif)
skb_queue_head_init(&rxq);
while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {
- int max_slots_needed;
+ RING_IDX max_slots_needed;
int i;
/* We need a cheap worse case estimate for the number of
@@ -510,9 +509,10 @@ static void xenvif_rx_action(struct xenvif *vif)
if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
skb_queue_head(&vif->rx_queue, skb);
need_to_notify = true;
- ring_full = true;
+ vif->rx_last_skb_slots = max_slots_needed;
break;
- }
+ } else
+ vif->rx_last_skb_slots = 0;
sco = (struct skb_cb_overlay *)skb->cb;
sco->meta_slots_used = xenvif_gop_skb(skb, &npo);
@@ -523,8 +523,6 @@ static void xenvif_rx_action(struct xenvif *vif)
BUG_ON(npo.meta_prod > ARRAY_SIZE(vif->meta));
- vif->rx_queue_stopped = !npo.copy_prod && ring_full;
-
if (!npo.copy_prod)
goto done;
@@ -1727,8 +1725,8 @@ static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif,
static inline int rx_work_todo(struct xenvif *vif)
{
- return (!skb_queue_empty(&vif->rx_queue) && !vif->rx_queue_stopped) ||
- vif->rx_event;
+ return !skb_queue_empty(&vif->rx_queue) &&
+ xenvif_rx_ring_slots_available(vif, vif->rx_last_skb_slots);
}
static inline int tx_work_todo(struct xenvif *vif)
@@ -1814,8 +1812,6 @@ int xenvif_kthread(void *data)
if (!skb_queue_empty(&vif->rx_queue))
xenvif_rx_action(vif);
- vif->rx_event = false;
-
if (skb_queue_empty(&vif->rx_queue) &&
netif_queue_stopped(vif->dev))
xenvif_start_queue(vif);
--
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