On Thu, May 20, 2021 at 06:16:11AM +0000, Rantala, Tommi T. (Nokia - FI/Espoo) wrote:
> On Mon, 2021-05-17 at 16:01 +0200, Greg Kroah-Hartman wrote:
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> [ Upstream commit 40cb881b5aaa0b69a7d93dec8440d5c62dae299f ]
>
> Hi Greg,
>
> There's fixup to this commit, hit the "unregister_netdevice" problems in 5.4.120
> while running kernel selftests.
>
> (also check the "Fixes:" tags, I think not all of them were yet included in 5.4.y)
>
>
> commit 0d7a7b2014b1a499a0fe24c9f3063d7856b5aaaf
> Author: Eric Dumazet <edumazet@xxxxxxxxxx>
> Date: Wed Mar 31 14:38:11 2021 -0700
>
> ipv6: remove extra dev_hold() for fallback tunnels
>
> My previous commits added a dev_hold() in tunnels ndo_init(),
> but forgot to remove it from special functions setting up fallback tunnels.
>
> Fallback tunnels do call their respective ndo_init()
>
> This leads to various reports like :
>
> unregister_netdevice: waiting for ip6gre0 to become free. Usage count = 2
>
> Fixes: 48bb5697269a ("ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods")
> Fixes: 6289a98f0817 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
> Fixes: 40cb881b5aaa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
> Fixes: 7f700334be9a ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
>
>
>
> After adopting CONFIG_PCPU_DEV_REFCNT=n option, syzbot was able to trigger
> a warning [1]
>
> Issue here is that:
>
> - all dev_put() should be paired with a corresponding prior dev_hold().
>
> - A driver doing a dev_put() in its ndo_uninit() MUST also
> do a dev_hold() in its ndo_init(), only when ndo_init()
> is returning 0.
>
> Otherwise, register_netdevice() would call ndo_uninit()
> in its error path and release a refcount too soon.
>
> Therefore, we need to move dev_hold() call from
> vti6_tnl_create2() to vti6_dev_init_gen()
>
> [1]
> WARNING: CPU: 0 PID: 15951 at lib/refcount.c:31
> refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
> Modules linked in:
> CPU: 0 PID: 15951 Comm: syz-executor.3 Not tainted 5.12.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
> Code: 1d 6a 5a e8 09 31 ff 89 de e8 8d 1a ab fd 84 db 75 e0 e8 d4 13 ab fd
> 48 c7 c7 a0 e1 c1 89 c6 05 4a 5a e8 09 01 e8 2e 36 fb 04 <0f> 0b eb c4 e8 b8
> 13 ab fd 0f b6 1d 39 5a e8 09 31 ff 89 de e8 58
> RSP: 0018:ffffc90001eaef28 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000040000 RSI: ffffffff815c51f5 RDI: fffff520003d5dd7
> RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffff815bdf8e R11: 0000000000000000 R12: ffff88801bb1c568
> R13: ffff88801f69e800 R14: 00000000ffffffff R15: ffff888050889d40
> FS: 00007fc79314e700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f1c1ff47108 CR3: 0000000020fd5000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> __refcount_dec include/linux/refcount.h:344 [inline]
> refcount_dec include/linux/refcount.h:359 [inline]
> dev_put include/linux/netdevice.h:4135 [inline]
> vti6_dev_uninit+0x31a/0x360 net/ipv6/ip6_vti.c:297
> register_netdevice+0xadf/0x1500 net/core/dev.c:10308
> vti6_tnl_create2+0x1b5/0x400 net/ipv6/ip6_vti.c:190
> vti6_newlink+0x9d/0xd0 net/ipv6/ip6_vti.c:1020
> __rtnl_newlink+0x1062/0x1710 net/core/rtnetlink.c:3443
> rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3491
> rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5553
> netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2502
> netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
> netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
> netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
> sock_sendmsg_nosec net/socket.c:654 [inline]
> sock_sendmsg+0xcf/0x120 net/socket.c:674
> ____sys_sendmsg+0x331/0x810 net/socket.c:2350
> ___sys_sendmsg+0xf3/0x170 net/socket.c:2404
> __sys_sendmmsg+0x195/0x470 net/socket.c:2490
> __do_sys_sendmmsg net/socket.c:2519 [inline]
> __se_sys_sendmmsg net/socket.c:2516 [inline]
> __x64_sys_sendmmsg+0x99/0x100 net/socket.c:2516
>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
> net/ipv6/ip6_vti.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
> index cc6180e08a4f..01ddb0f70c57 100644
> --- a/net/ipv6/ip6_vti.c
> +++ b/net/ipv6/ip6_vti.c
> @@ -192,7 +192,6 @@ static int vti6_tnl_create2(struct net_device *dev)
>
> strcpy(t->parms.name, dev->name);
>
> - dev_hold(dev);
> vti6_tnl_link(ip6n, t);
>
> return 0;
> @@ -921,6 +920,7 @@ static inline int vti6_dev_init_gen(struct net_device
> *dev)
> dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
> if (!dev->tstats)
> return -ENOMEM;
> + dev_hold(dev);
> return 0;
> }
>
I do not understand, what needs to be done here?
greg k-h
