Subject: [PATCH 25/34] hv_netvsc: fix race in napi poll when rescheduling

From: Stephen Hemminger <[email-masked]>
Date: Mon, 14 May 2018 15:32:13 -0700

[ Commit d64e38ae690e3337db0d38d9b149a193a1646c4b upstream. ]

There is a race between napi_reschedule and re-enabling interrupts
which could lead to missed host interrrupts.  This occurs when
interrupts are re-enabled (hv_end_read) and vmbus irq callback
(netvsc_channel_cb) has already scheduled NAPI.

Signed-off-by: Stephen Hemminger <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 drivers/net/hyperv/netvsc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index b7720b65f5d6..7e0eb99571af 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1205,9 +1205,10 @@ int netvsc_poll(struct napi_struct *napi, int budget)
 	if (send_recv_completions(ndev, net_device, nvchan) == 0 &&
 	    work_done < budget &&
 	    napi_complete_done(napi, work_done) &&
-	    hv_end_read(&channel->inbound)) {
+	    hv_end_read(&channel->inbound) &&
+	    napi_schedule_prep(napi)) {
 		hv_begin_read(&channel->inbound);
-		napi_reschedule(napi);
+		__napi_schedule(napi);
 	}
 
 	/* Driver may overshoot since multiple packets per descriptor */
-- 
2.14.3