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net: make netdev_for_each_lower_dev safe for device removal
When I used netdev_for_each_lower_dev in commit bad53162 ("vrf: remove slave queue and private slave struct") I thought that it acts like netdev_for_each_lower_private and can be used to remove the current device from the list while walking, but unfortunately it acts more like netdev_for_each_lower_private_rcu and doesn't allow it. The difference is where the "iter" points to, right now it points to the current element and that makes it impossible to remove it. Change the logic to be similar to netdev_for_each_lower_private and make it point to the "next" element so we can safely delete the current one. VRF is the only such user right now, there's no change for the read-only users. Here's what can happen now: [98423.249858] general protection fault: 0000 [#1] SMP [98423.250175] Modules linked in: vrf bridge(O) stp llc nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace sunrpc crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel jitterentropy_rng sha256_generic hmac drbg ppdev aesni_intel aes_x86_64 glue_helper lrw gf128mul ablk_helper cryptd evdev serio_raw pcspkr virtio_balloon parport_pc parport i2c_piix4 i2c_core virtio_console acpi_cpufreq button 9pnet_virtio 9p 9pnet fscache ipv6 autofs4 ext4 crc16 mbcache jbd2 sg virtio_blk virtio_net sr_mod cdrom e1000 ata_generic ehci_pci uhci_hcd ehci_hcd usbcore usb_common virtio_pci ata_piix libata floppy virtio_ring virtio scsi_mod [last unloaded: bridge] [98423.255040] CPU: 1 PID: 14173 Comm: ip Tainted: G O 4.5.0-rc2+ #81 [98423.255386] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014 [98423.255777] task: ffff8800547f5540 ti: ffff88003428c000 task.ti: ffff88003428c000 [98423.256123] RIP: 0010:[<ffffffff81514f3e>] [<ffffffff81514f3e>] netdev_lower_get_next+0x1e/0x30 [98423.256534] RSP: 0018:ffff88003428f940 EFLAGS: 00010207 [98423.256766] RAX: 0002000100000004 RBX: ffff880054ff9000 RCX: 0000000000000000 [98423.257039] RDX: ffff88003428f8b8 RSI: ffff88003428f950 RDI: ffff880054ff90c0 [98423.257287] RBP: ffff88003428f940 R08: 0000000000000000 R09: 0000000000000000 [98423.257537] R10: 0000000000000001 R11: 0000000000000000 R12: ffff88003428f9e0 [98423.257802] R13: ffff880054a5fd00 R14: ffff88003428f970 R15: 0000000000000001 [98423.258055] FS: 00007f3d76881700(0000) GS:ffff88005d000000(0000) knlGS:0000000000000000 [98423.258418] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [98423.258650] CR2: 00007ffe5951ffa8 CR3: 0000000052077000 CR4: 00000000000406e0 [98423.258902] Stack: [98423.259075] ffff88003428f960 ffffffffa0442636 0002000100000004 ffff880054ff9000 [98423.259647] ffff88003428f9b0 ffffffff81518205 ffff880054ff9000 ffff88003428f978 [98423.260208] ffff88003428f978 ffff88003428f9e0 ffff88003428f9e0 ffff880035b35f00 [98423.260739] Call Trace: [98423.260920] [<ffffffffa0442636>] vrf_dev_uninit+0x76/0xa0 [vrf] [98423.261156] [<ffffffff81518205>] rollback_registered_many+0x205/0x390 [98423.261401] [<ffffffff815183ec>] unregister_netdevice_many+0x1c/0x70 [98423.261641] [<ffffffff8153223c>] rtnl_delete_link+0x3c/0x50 [98423.271557] [<ffffffff815335bb>] rtnl_dellink+0xcb/0x1d0 [98423.271800] [<ffffffff811cd7da>] ? __inc_zone_state+0x4a/0x90 [98423.272049] [<ffffffff815337b4>] rtnetlink_rcv_msg+0x84/0x200 [98423.272279] [<ffffffff810cfe7d>] ? trace_hardirqs_on+0xd/0x10 [98423.272513] [<ffffffff8153370b>] ? rtnetlink_rcv+0x1b/0x40 [98423.272755] [<ffffffff81533730>] ? rtnetlink_rcv+0x40/0x40 [98423.272983] [<ffffffff8155d6e7>] netlink_rcv_skb+0x97/0xb0 [98423.273209] [<ffffffff8153371a>] rtnetlink_rcv+0x2a/0x40 [98423.273476] [<ffffffff8155ce8b>] netlink_unicast+0x11b/0x1a0 [98423.273710] [<ffffffff8155d2f1>] netlink_sendmsg+0x3e1/0x610 [98423.273947] [<ffffffff814fbc98>] sock_sendmsg+0x38/0x70 [98423.274175] [<ffffffff814fc253>] ___sys_sendmsg+0x2e3/0x2f0 [98423.274416] [<ffffffff810d841e>] ? do_raw_spin_unlock+0xbe/0x140 [98423.274658] [<ffffffff811e1bec>] ? handle_mm_fault+0x26c/0x2210 [98423.274894] [<ffffffff811e19cd>] ? handle_mm_fault+0x4d/0x2210 [98423.275130] [<ffffffff81269611>] ? __fget_light+0x91/0xb0 [98423.275365] [<ffffffff814fcd42>] __sys_sendmsg+0x42/0x80 [98423.275595] [<ffffffff814fcd92>] SyS_sendmsg+0x12/0x20 [98423.275827] [<ffffffff81611bb6>] entry_SYSCALL_64_fastpath+0x16/0x7a [98423.276073] Code: c3 31 c0 5d c3 0f 1f 84 00 00 00 00 00 66 66 66 66 90 48 8b 06 55 48 81 c7 c0 00 00 00 48 89 e5 48 8b 00 48 39 f8 74 09 48 89 06 <48> 8b 40 e8 5d c3 31 c0 5d c3 0f 1f 84 00 00 00 00 00 66 66 66 [98423.279639] RIP [<ffffffff81514f3e>] netdev_lower_get_next+0x1e/0x30 [98423.279920] RSP <ffff88003428f940> CC: David Ahern <dsa@cumulusnetworks.com> CC: David S. Miller <davem@davemloft.net> CC: Roopa Prabhu <roopa@cumulusnetworks.com> CC: Vlad Yasevich <vyasevic@redhat.com> Fixes: bad53162 ("vrf: remove slave queue and private slave struct") Signed-off-by:Nikolay Aleksandrov <nikolay@cumulusnetworks.com> Reviewed-by: