From 0d08fceb2e21c30ca3e1e462e678723f806acf18 Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel@citrix.com>
Date: Fri, 16 May 2014 12:26:04 +0100
Subject: xen-netback: fix race between napi_complete() and interrupt handler
When the NAPI budget was not all used, xenvif_poll() would call
napi_complete() /after/ enabling the interrupt. This resulted in a
race between the napi_complete() and the napi_schedule() in the
interrupt handler. The use of local_irq_save/restore() avoided by
race iff the handler is running on the same CPU but not if it was
running on a different CPU.
Fix this properly by calling napi_complete() before reenabling
interrupts (in the xenvif_napi_schedule_or_enable_irq() call).
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
drivers/net/xen-netback/interface.c | 30 +++---------------------------
1 file changed, 3 insertions(+), 27 deletions(-)
(limited to 'drivers/net/xen-netback/interface.c')
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index ef05c5c49d41..20e9defa1060 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -75,32 +75,8 @@ static int xenvif_poll(struct napi_struct *napi, int budget)
work_done = xenvif_tx_action(vif, budget);
if (work_done < budget) {
- int more_to_do = 0;
- unsigned long flags;
-
- /* It is necessary to disable IRQ before calling
- * RING_HAS_UNCONSUMED_REQUESTS. Otherwise we might
- * lose event from the frontend.
- *
- * Consider:
- * RING_HAS_UNCONSUMED_REQUESTS
- * <frontend generates event to trigger napi_schedule>
- * __napi_complete
- *
- * This handler is still in scheduled state so the
- * event has no effect at all. After __napi_complete
- * this handler is descheduled and cannot get
- * scheduled again. We lose event in this case and the ring
- * will be completely stalled.
- */
-
- local_irq_save(flags);
-
- RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);
- if (!more_to_do)
- __napi_complete(napi);
-
- local_irq_restore(flags);
+ napi_complete(napi);
+ xenvif_napi_schedule_or_enable_events(vif);
}
return work_done;
@@ -194,7 +170,7 @@ static void xenvif_up(struct xenvif *vif)
enable_irq(vif->tx_irq);
if (vif->tx_irq != vif->rx_irq)
enable_irq(vif->rx_irq);
- xenvif_check_rx_xenvif(vif);
+ xenvif_napi_schedule_or_enable_events(vif);
}
static void xenvif_down(struct xenvif *vif)
--
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