linux-kernel - [PATCH net v2] hv_netvsc: Fix a warning of suspicious RCU usage

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Message-ID: <PU1P153MB0169A6492DCBB490FE7FE52CBFD60@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>
Date:   Fri, 9 Aug 2019 01:58:08 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     "sashal@...nel.org" <sashal@...nel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        vkuznets <vkuznets@...hat.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>
Subject: [PATCH net v2] hv_netvsc: Fix a warning of suspicious RCU usage


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

Fixes: 776e726bfb34 ("netvsc: fix RCU warning in get_stats")
Signed-off-by: Dexuan Cui <decui@...rosoft.com>
---

Changes in v2:
    Made the minimal required change.
	Added a Fixes tag.
	Removed Stephen H.'s Signed-off-by since this is somewhat different from the 
		v1 from him; if there is any bug in v2, it's all my fault. :-)

 drivers/net/hyperv/netvsc_drv.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index f9209594624b..b6357a75712c 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -1240,12 +1240,15 @@ 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 = rcu_dereference_rtnl(ndev_ctx->nvdev);
+	struct netvsc_device *nvdev;
 	struct netvsc_vf_pcpu_stats vf_tot;
 	int i;
 
+	rcu_read_lock();
+
+	nvdev = rcu_dereference(ndev_ctx->nvdev);
 	if (!nvdev)
-		return;
+		goto out;
 
 	netdev_stats_to_stats64(t, &net->stats);
 
@@ -1284,6 +1287,8 @@ static void netvsc_get_stats64(struct net_device *net,
 		t->rx_packets	+= packets;
 		t->multicast	+= multicast;
 	}
+out:
+	rcu_read_unlock();
 }
 
 static int netvsc_set_mac_addr(struct net_device *ndev, void *p)
-- 
2.19.1