Subject: [PATCH 04/23] net: avoid weird emergency message

From: Eric Dumazet <[email-masked]>
Date: Thu, 16 May 2019 08:09:57 -0700

[ Upstream commit d7c04b05c9ca14c55309eb139430283a45c4c25f ]

When host is under high stress, it is very possible thread
running netdev_wait_allrefs() returns from msleep(250)
10 seconds late.

This leads to these messages in the syslog :

[...] unregister_netdevice: waiting for syz_tun to become free. Usage count = 0

If the device refcount is zero, the wait is over.

Signed-off-by: Eric Dumazet <[email-masked]>
Reported-by: syzbot <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index f409406254dd..255f99cb7c48 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8911,7 +8911,7 @@ static void netdev_wait_allrefs(struct net_device *dev)
 
 		refcnt = netdev_refcnt_read(dev);
 
-		if (time_after(jiffies, warning_time + 10 * HZ)) {
+		if (refcnt && time_after(jiffies, warning_time + 10 * HZ)) {
 			pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
 				 dev->name, refcnt);
 			warning_time = jiffies;
-- 
2.20.1