hv_netvsc: fix race in napi poll when rescheduling

BugLink: http://bugs.launchpad.net/bugs/1783418
[ 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 <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index 0c3f587884110e624394b48864d3faca736cef68..83b291f3e7410544898e86623cc861f41587e1fc 100644 (file)
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1213,9 +1213,10 @@ 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 */