[PATCH net] hv_netvsc: Fix a warning of suspicious RCU usage

[PATCH net] hv_netvsc: Fix a warning of suspicious RCU usage

[Dexuan Cui]

This fixes a warning of "suspicious rcu_dereference_check() usage"
when nload runs.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 drivers/net/hyperv/netvsc_drv.c | 44 +++++++++++++++++++--------------
 1 file changed, 26 insertions(+), 18 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index f9209594624b5..25502d335b94f 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -1236,25 +1236,10 @@ static void netvsc_get_pcpu_stats(struct net_device *net,
 	}
 }
 
-static void netvsc_get_stats64(struct net_device *net,
-			       struct rtnl_link_stats64 *t)
+static void netvsc_get_per_chan_stats(struct netvsc_device *nvdev,
+				      struct rtnl_link_stats64 *t)
 {
-	struct net_device_context *ndev_ctx = netdev_priv(net);
-	struct netvsc_device *nvdev = rcu_dereference_rtnl(ndev_ctx->nvdev);
-	struct netvsc_vf_pcpu_stats vf_tot;
-	int i;
-
-	if (!nvdev)
-		return;
-
-	netdev_stats_to_stats64(t, &net->stats);
-
-	netvsc_get_vf_stats(net, &vf_tot);
-	t->rx_packets += vf_tot.rx_packets;
-	t->tx_packets += vf_tot.tx_packets;
-	t->rx_bytes   += vf_tot.rx_bytes;
-	t->tx_bytes   += vf_tot.tx_bytes;
-	t->tx_dropped += vf_tot.tx_dropped;
+	u32 i;
 
 	for (i = 0; i < nvdev->num_chn; i++) {
 		const struct netvsc_channel *nvchan = &nvdev->chan_table[i];
@@ -1286,6 +1271,29 @@ static void netvsc_get_stats64(struct net_device *net,
 	}
 }
 
+static void netvsc_get_stats64(struct net_device *net,
+			       struct rtnl_link_stats64 *t)
+{
+	struct net_device_context *ndev_ctx = netdev_priv(net);
+	struct netvsc_device *nvdev;
+	struct netvsc_vf_pcpu_stats vf_tot;
+
+	netdev_stats_to_stats64(t, &net->stats);
+
+	netvsc_get_vf_stats(net, &vf_tot);
+	t->rx_packets += vf_tot.rx_packets;
+	t->tx_packets += vf_tot.tx_packets;
+	t->rx_bytes   += vf_tot.rx_bytes;
+	t->tx_bytes   += vf_tot.tx_bytes;
+	t->tx_dropped += vf_tot.tx_dropped;
+
+	rcu_read_lock();
+	nvdev = rcu_dereference(ndev_ctx->nvdev);
+	if (nvdev)
+		netvsc_get_per_chan_stats(nvdev, t);
+	rcu_read_unlock();
+}
+
 static int netvsc_set_mac_addr(struct net_device *ndev, void *p)
 {
 	struct net_device_context *ndc = netdev_priv(ndev);

Re: [PATCH net] hv_netvsc: Fix a warning of suspicious RCU usage

[Jakub Kicinski]

On Tue, 6 Aug 2019 05:17:44 +0000, Dexuan Cui wrote:
> This fixes a warning of "suspicious rcu_dereference_check() usage"
> when nload runs.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> Signed-off-by: Dexuan Cui <decui@microsoft.com>

Minor change in behaviour would perhaps be worth acknowledging in the
commit message (since you check ndev for NULL later now), and a Fixes
tag would be good.

But the looks pretty straightforward and correct!

RE: [PATCH net] hv_netvsc: Fix a warning of suspicious RCU usage

[Dexuan Cui]

> From: Jakub Kicinski <jakub.kicinski@netronome.com>
> Sent: Tuesday, August 6, 2019 12:13 PM
> To: Dexuan Cui <decui@microsoft.com>
> 
> On Tue, 6 Aug 2019 05:17:44 +0000, Dexuan Cui wrote:
> > This fixes a warning of "suspicious rcu_dereference_check() usage"
> > when nload runs.
> >
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > Signed-off-by: Dexuan Cui <decui@microsoft.com>
> 
> Minor change in behaviour would perhaps be worth acknowledging in the
> commit message (since you check ndev for NULL later now), and a Fixes
> tag would be good.
> 
> But the looks pretty straightforward and correct!

Hi,
Yeah, it looks the minor behavior change doesn't matter, because IMO the 
'nvdev' can only be NULL when the NIC is being removed, or the MTU is
being changed, etc.

The Fixes tag is:
Fixes: 776e726bfb34 ("netvsc: fix RCU warning in get_stats")

If I should send a v2, please let me know.

Thanks,
-- Dexuan

Re: [PATCH net] hv_netvsc: Fix a warning of suspicious RCU usage

[David Miller]

From: Dexuan Cui <decui@microsoft.com>
Date: Tue, 6 Aug 2019 05:17:44 +0000

> 
> This fixes a warning of "suspicious rcu_dereference_check() usage"
> when nload runs.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> Signed-off-by: Dexuan Cui <decui@microsoft.com>

Please resend with appropriate fixes tag.

RE: [PATCH net] hv_netvsc: Fix a warning of suspicious RCU usage

[Dexuan Cui]

> From: David Miller <davem@davemloft.net>
> Sent: Thursday, August 8, 2019 6:14 PM
> To: Dexuan Cui <decui@microsoft.com>
> Cc: netdev@vger.kernel.org; Haiyang Zhang <haiyangz@microsoft.com>;
> Stephen Hemminger <sthemmin@microsoft.com>; sashal@kernel.org; KY
> Srinivasan <kys@microsoft.com>; Michael Kelley <mikelley@microsoft.com>;
> linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com; vkuznets
> <vkuznets@redhat.com>; marcelo.cerri@canonical.com
> Subject: Re: [PATCH net] hv_netvsc: Fix a warning of suspicious RCU usage
> 
> From: Dexuan Cui <decui@microsoft.com>
> Date: Tue, 6 Aug 2019 05:17:44 +0000
> 
> >
> > This fixes a warning of "suspicious rcu_dereference_check() usage"
> > when nload runs.
> >
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > Signed-off-by: Dexuan Cui <decui@microsoft.com>
> 
> Please resend with appropriate fixes tag.

Will do shortly.

Thanks,
-- Dexuan