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Recent updates to the locking mechanism that protects IPv6 routing tables [1] have affected the SRv6 networking subsystem. Such changes cause problems with some SRv6 Endpoints behaviors, like End.B6.Encaps and also impact SRv6 counters. Starting from commit169fd62799("ipv6: Get rid of RTNL for SIOCADDRT and RTM_NEWROUTE."), the inet6_rtm_newroute() function no longer needs to acquire the RTNL lock for creating and configuring IPv6 routes and set up lwtunnels. The RTNL lock can be avoided because the ip6_route_add() function finishes setting up a new route in a section protected by RCU. This makes sure that no dev/nexthops can disappear during the operation. Because of this, the steps for setting up lwtunnels - i.e., calling lwtunnel_build_state() - are now done in a RCU lock section and not under the RTNL lock anymore. However, creating and configuring a lwtunnel instance in an RCU-protected section can be problematic when that tunnel needs to allocate memory using the GFP_KERNEL flag. For example, the following trace shows what happens when an SRv6 End.B6.Encaps behavior is instantiated after commit169fd62799("ipv6: Get rid of RTNL for SIOCADDRT and RTM_NEWROUTE."): [ 3061.219696] BUG: sleeping function called from invalid context at ./include/linux/sched/mm.h:321 [ 3061.226136] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 445, name: ip [ 3061.232101] preempt_count: 0, expected: 0 [ 3061.235414] RCU nest depth: 1, expected: 0 [ 3061.238622] 1 lock held by ip/445: [ 3061.241458] #0: ffffffff83ec64a0 (rcu_read_lock){....}-{1:3}, at: ip6_route_add+0x41/0x1e0 [ 3061.248520] CPU: 1 UID: 0 PID: 445 Comm: ip Not tainted 6.15.0-rc3-micro-vm-dev-00590-ge527e891492d #2058 PREEMPT(full) [ 3061.248532] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 [ 3061.248549] Call Trace: [ 3061.248620] <TASK> [ 3061.248633] dump_stack_lvl+0xa9/0xc0 [ 3061.248846] __might_resched+0x218/0x360 [ 3061.248871] __kmalloc_node_track_caller_noprof+0x332/0x4e0 [ 3061.248889] ? rcu_is_watching+0x3a/0x70 [ 3061.248902] ? parse_nla_srh+0x56/0xa0 [ 3061.248938] kmemdup_noprof+0x1c/0x40 [ 3061.248952] parse_nla_srh+0x56/0xa0 [ 3061.248969] seg6_local_build_state+0x2e0/0x580 [ 3061.248992] ? __lock_acquire+0xaff/0x1cd0 [ 3061.249013] ? do_raw_spin_lock+0x111/0x1d0 [ 3061.249027] ? __pfx_seg6_local_build_state+0x10/0x10 [ 3061.249068] ? lwtunnel_build_state+0xe1/0x3a0 [ 3061.249274] lwtunnel_build_state+0x10d/0x3a0 [ 3061.249303] fib_nh_common_init+0xce/0x1e0 [ 3061.249337] ? __pfx_fib_nh_common_init+0x10/0x10 [ 3061.249352] ? in6_dev_get+0xaf/0x1f0 [ 3061.249369] ? __rcu_read_unlock+0x64/0x2e0 [ 3061.249392] fib6_nh_init+0x290/0xc30 [ 3061.249422] ? __pfx_fib6_nh_init+0x10/0x10 [ 3061.249447] ? __lock_acquire+0xaff/0x1cd0 [ 3061.249459] ? _raw_spin_unlock_irqrestore+0x22/0x70 [ 3061.249624] ? ip6_route_info_create+0x423/0x520 [ 3061.249641] ? rcu_is_watching+0x3a/0x70 [ 3061.249683] ip6_route_info_create_nh+0x190/0x390 [ 3061.249715] ip6_route_add+0x71/0x1e0 [ 3061.249730] ? __pfx_inet6_rtm_newroute+0x10/0x10 [ 3061.249743] inet6_rtm_newroute+0x426/0xc50 [ 3061.249764] ? avc_has_perm_noaudit+0x13d/0x360 [ 3061.249853] ? __pfx_inet6_rtm_newroute+0x10/0x10 [ 3061.249905] ? __lock_acquire+0xaff/0x1cd0 [ 3061.249962] ? rtnetlink_rcv_msg+0x52f/0x890 [ 3061.249996] ? __pfx_inet6_rtm_newroute+0x10/0x10 [ 3061.250012] rtnetlink_rcv_msg+0x551/0x890 [ 3061.250040] ? __pfx_rtnetlink_rcv_msg+0x10/0x10 [ 3061.250065] ? __lock_acquire+0xaff/0x1cd0 [ 3061.250092] netlink_rcv_skb+0xbd/0x1f0 [ 3061.250108] ? __pfx_rtnetlink_rcv_msg+0x10/0x10 [ 3061.250124] ? __pfx_netlink_rcv_skb+0x10/0x10 [ 3061.250179] ? netlink_deliver_tap+0x10b/0x700 [ 3061.250210] netlink_unicast+0x2e7/0x410 [ 3061.250232] ? __pfx_netlink_unicast+0x10/0x10 [ 3061.250241] ? __lock_acquire+0xaff/0x1cd0 [ 3061.250280] netlink_sendmsg+0x366/0x670 [ 3061.250306] ? __pfx_netlink_sendmsg+0x10/0x10 [ 3061.250313] ? find_held_lock+0x2d/0xa0 [ 3061.250344] ? import_ubuf+0xbc/0xf0 [ 3061.250370] ? __pfx_netlink_sendmsg+0x10/0x10 [ 3061.250381] __sock_sendmsg+0x13e/0x150 [ 3061.250420] ____sys_sendmsg+0x33d/0x450 [ 3061.250442] ? __pfx_____sys_sendmsg+0x10/0x10 [ 3061.250453] ? __pfx_copy_msghdr_from_user+0x10/0x10 [ 3061.250489] ? __pfx_slab_free_after_rcu_debug+0x10/0x10 [ 3061.250514] ___sys_sendmsg+0xe5/0x160 [ 3061.250530] ? __pfx____sys_sendmsg+0x10/0x10 [ 3061.250568] ? __lock_acquire+0xaff/0x1cd0 [ 3061.250617] ? find_held_lock+0x2d/0xa0 [ 3061.250678] ? __virt_addr_valid+0x199/0x340 [ 3061.250704] ? preempt_count_sub+0xf/0xc0 [ 3061.250736] __sys_sendmsg+0xca/0x140 [ 3061.250750] ? __pfx___sys_sendmsg+0x10/0x10 [ 3061.250786] ? syscall_exit_to_user_mode+0xa2/0x1e0 [ 3061.250825] do_syscall_64+0x62/0x140 [ 3061.250844] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 3061.250855] RIP: 0033:0x7f0b042ef914 [ 3061.250868] Code: 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b5 0f 1f 80 00 00 00 00 48 8d 05 e9 5d 0c 00 8b 00 85 c0 75 13 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 41 54 41 89 d4 55 48 89 f5 53 [ 3061.250876] RSP: 002b:00007ffc2d113ef8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e [ 3061.250885] RAX: ffffffffffffffda RBX: 00000000680f93fa RCX: 00007f0b042ef914 [ 3061.250891] RDX: 0000000000000000 RSI: 00007ffc2d113f60 RDI: 0000000000000003 [ 3061.250897] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000008 [ 3061.250902] R10: fffffffffffff26d R11: 0000000000000246 R12: 0000000000000001 [ 3061.250907] R13: 000055a961f8a520 R14: 000055a961f63eae R15: 00007ffc2d115270 [ 3061.250952] </TASK> To solve this issue, we replace the GFP_KERNEL flag with the GFP_ATOMIC one in those SRv6 Endpoints that need to allocate memory during the setup phase. This change makes sure that memory allocations are handled in a way that works with RCU critical sections. [1] - https://lore.kernel.org/all/20250418000443.43734-1-kuniyu@amazon.com/ Fixes:169fd62799("ipv6: Get rid of RTNL for SIOCADDRT and RTM_NEWROUTE.") Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it> Reviewed-by: David Ahern <dsahern@kernel.org> Link: https://patch.msgid.link/20250429132453.31605-1-andrea.mayer@uniroma2.it Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
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