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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
        syzbot <syzkaller@googlegroups.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.9 01/53] net: avoid weird emergency message
Date:   Thu, 23 May 2019 21:05:25 +0200
Message-Id: <20190523181711.173625689@linuxfoundation.org>
In-Reply-To: <20190523181710.981455400@linuxfoundation.org>
References: <20190523181710.981455400@linuxfoundation.org>
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From: Eric Dumazet <edumazet@google.com>

[ 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 <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/dev.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7499,7 +7499,7 @@ static void netdev_wait_allrefs(struct n
 
 		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;