netdev - [PATCH net 5/9] hv_netvsc: fix race in napi poll when rescheduling

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Message-Id: <20180301182756.23027-6-sthemmin@microsoft.com>
Date:   Thu,  1 Mar 2018 10:27:52 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com
Cc:     devel@...uxdriverproject.org, netdev@...r.kernel.org
Subject: [PATCH net 5/9] hv_netvsc: fix race in napi poll when rescheduling

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 <sthemmin@...rosoft.com>
---
 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 ff97a85b2e9d..4237cedc4f08 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1207,9 +1207,10 @@ 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 */
-- 
2.16.1