netdev - [PATCH next] loopback: fix lockdep splat

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Date:   Tue,  2 Jul 2019 23:16:31 -0700
From:   Mahesh Bandewar <maheshb@...gle.com>
To:     Netdev <netdev@...r.kernel.org>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Mahesh Bandewar <mahesh@...dewar.net>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH next] loopback: fix lockdep splat

dev_init_scheduler() and dev_activate() expect the caller to
hold RTNL. Since we don't want blackhole device to be initialized
per ns, we are initializing at init.

[    3.855027] Call Trace:
[    3.855034]  dump_stack+0x67/0x95
[    3.855037]  lockdep_rcu_suspicious+0xd5/0x110
[    3.855044]  dev_init_scheduler+0xe3/0x120
[    3.855048]  ? net_olddevs_init+0x60/0x60
[    3.855050]  blackhole_netdev_init+0x45/0x6e
[    3.855052]  do_one_initcall+0x6c/0x2fa
[    3.855058]  ? rcu_read_lock_sched_held+0x8c/0xa0
[    3.855066]  kernel_init_freeable+0x1e5/0x288
[    3.855071]  ? rest_init+0x260/0x260
[    3.855074]  kernel_init+0xf/0x180
[    3.855076]  ? rest_init+0x260/0x260
[    3.855078]  ret_from_fork+0x24/0x30

Fixes: 4de83b88c66 ("loopback: create blackhole net device similar to loopack.")
Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
---
 drivers/net/loopback.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index 3b39def5471e..14545a8797a8 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -261,8 +261,10 @@ static int __init blackhole_netdev_init(void)
 	if (!blackhole_netdev)
 		return -ENOMEM;
 
+	rtnl_lock();
 	dev_init_scheduler(blackhole_netdev);
 	dev_activate(blackhole_netdev);
+	rtnl_unlock();
 
 	blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
 	dev_net_set(blackhole_netdev, &init_net);
-- 
2.22.0.410.gd8fdbe21b5-goog