On 11/5/24 6:02 PM, Omid Ehtemam-Haghighi wrote:
> Soft lockups have been observed on a cluster of Linux-based edge routers
> located in a highly dynamic environment. Using the `bird` service, these
> routers continuously update BGP-advertised routes due to frequently
> changing nexthop destinations, while also managing significant IPv6
> traffic. The lockups occur during the traversal of the multipath
> circular linked-list in the `fib6_select_path` function, particularly
> while iterating through the siblings in the list. The issue typically
> arises when the nodes of the linked list are unexpectedly deleted
> concurrently on a different core—indicated by their 'next' and
> 'previous' elements pointing back to the node itself and their reference
> count dropping to zero. This results in an infinite loop, leading to a
> soft lockup that triggers a system panic via the watchdog timer.
>
> Apply RCU primitives in the problematic code sections to resolve the
> issue. Where necessary, update the references to fib6_siblings to
> annotate or use the RCU APIs.
>
> Include a test script that reproduces the issue. The script
> periodically updates the routing table while generating a heavy load
> of outgoing IPv6 traffic through multiple iperf3 clients. It
> consistently induces infinite soft lockups within a couple of minutes.
>
> Kernel log:
>
> 0 [ffffbd13003e8d30] machine_kexec at ffffffff8ceaf3eb
> 1 [ffffbd13003e8d90] __crash_kexec at ffffffff8d0120e3
> 2 [ffffbd13003e8e58] panic at ffffffff8cef65d4
> 3 [ffffbd13003e8ed8] watchdog_timer_fn at ffffffff8d05cb03
> 4 [ffffbd13003e8f08] __hrtimer_run_queues at ffffffff8cfec62f
> 5 [ffffbd13003e8f70] hrtimer_interrupt at ffffffff8cfed756
> 6 [ffffbd13003e8fd0] __sysvec_apic_timer_interrupt at ffffffff8cea01af
> 7 [ffffbd13003e8ff0] sysvec_apic_timer_interrupt at ffffffff8df1b83d
> -- <IRQ stack> --
> 8 [ffffbd13003d3708] asm_sysvec_apic_timer_interrupt at ffffffff8e000ecb
> [exception RIP: fib6_select_path+299]
> RIP: ffffffff8ddafe7b RSP: ffffbd13003d37b8 RFLAGS: 00000287
> RAX: ffff975850b43600 RBX: ffff975850b40200 RCX: 0000000000000000
> RDX: 000000003fffffff RSI: 0000000051d383e4 RDI: ffff975850b43618
> RBP: ffffbd13003d3800 R8: 0000000000000000 R9: ffff975850b40200
> R10: 0000000000000000 R11: 0000000000000000 R12: ffffbd13003d3830
> R13: ffff975850b436a8 R14: ffff975850b43600 R15: 0000000000000007
> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> 9 [ffffbd13003d3808] ip6_pol_route at ffffffff8ddb030c
> 10 [ffffbd13003d3888] ip6_pol_route_input at ffffffff8ddb068c
> 11 [ffffbd13003d3898] fib6_rule_lookup at ffffffff8ddf02b5
> 12 [ffffbd13003d3928] ip6_route_input at ffffffff8ddb0f47
> 13 [ffffbd13003d3a18] ip6_rcv_finish_core.constprop.0 at ffffffff8dd950d0
> 14 [ffffbd13003d3a30] ip6_list_rcv_finish.constprop.0 at ffffffff8dd96274
> 15 [ffffbd13003d3a98] ip6_sublist_rcv at ffffffff8dd96474
> 16 [ffffbd13003d3af8] ipv6_list_rcv at ffffffff8dd96615
> 17 [ffffbd13003d3b60] __netif_receive_skb_list_core at ffffffff8dc16fec
> 18 [ffffbd13003d3be0] netif_receive_skb_list_internal at ffffffff8dc176b3
> 19 [ffffbd13003d3c50] napi_gro_receive at ffffffff8dc565b9
> 20 [ffffbd13003d3c80] ice_receive_skb at ffffffffc087e4f5 [ice]
> 21 [ffffbd13003d3c90] ice_clean_rx_irq at ffffffffc0881b80 [ice]
> 22 [ffffbd13003d3d20] ice_napi_poll at ffffffffc088232f [ice]
> 23 [ffffbd13003d3d80] __napi_poll at ffffffff8dc18000
> 24 [ffffbd13003d3db8] net_rx_action at ffffffff8dc18581
> 25 [ffffbd13003d3e40] __do_softirq at ffffffff8df352e9
> 26 [ffffbd13003d3eb0] run_ksoftirqd at ffffffff8ceffe47
> 27 [ffffbd13003d3ec0] smpboot_thread_fn at ffffffff8cf36a30
> 28 [ffffbd13003d3ee8] kthread at ffffffff8cf2b39f
> 29 [ffffbd13003d3f28] ret_from_fork at ffffffff8ce5fa64
> 30 [ffffbd13003d3f50] ret_from_fork_asm at ffffffff8ce03cbb
>
> Fixes: 66f5d6ce53e6 ("ipv6: replace rwlock with rcu and spinlock in fib6_table")
> Reported-by: Adrian Oliver <kernel@xxxxxxxxxx>
> Signed-off-by: Omid Ehtemam-Haghighi <omid.ehtemamhaghighi@xxxxxxxxxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: David Ahern <dsahern@xxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: Shuah Khan <shuah@xxxxxxxxxx>
> Cc: Ido Schimmel <idosch@xxxxxxxxxx>
> Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> Cc: Simon Horman <horms@xxxxxxxxxx>
> Cc: Omid Ehtemam-Haghighi <oeh.kernel@xxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: linux-kselftest@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> v6 -> v7:
> * Rebased on top of 'net-next'
>
> v5 -> v6:
> * Adjust the comment line lengths in the test script to a maximum of
> 80 characters
> * Change memory allocation in inet6_rt_notify from gfp_any() to GFP_ATOMIC for
> atomic allocation in non-blocking contexts, as suggested by Ido Schimmel
> * NOTE: I have executed the test script on both bare-metal servers and
> virtualized environments such as QEMU and vng. In the case of bare-metal, it
> consistently triggers a soft lockup in under a minute on unpatched kernels.
> For the virtualized environments, an unpatched kernel compiled with the
> Ubuntu 24.04 configuration also triggers a soft lockup, though it takes
> longer; however, it did not trigger a soft lockup on kernels compiled with
> configurations provided in:
>
> https://github.com/linux-netdev/nipa/wiki/How-to-run-netdev-selftests-CI-style
>
> leading to potential false negatives in the test results.
>
> I am curious if this test can be executed on a bare-metal machine within a
> CI system, if such a setup exists, rather than in a virtualized environment.
> If that’s not possible, how can I apply a different kernel configuration,
> such as the one used in Ubuntu 24.04, for this test? Please advise.
>
> v4 -> v5:
> * Addressed review comments from Paolo Abeni.
> * Added additional clarifying comments in the test script.
> * Minor cleanup performed in the test script.
>
> v3 -> v4:
> * Added RCU primitives to rt6_fill_node(). I found that this function is typically
> called either with a table lock held or within rcu_read_lock/rcu_read_unlock
> pairs, except in the following call chain, where the protection is unclear:
>
> rt_fill_node()
> fib6_info_hw_flags_set()
> mlxsw_sp_fib6_offload_failed_flag_set()
> mlxsw_sp_router_fib6_event_work()
>
> The last function is initialized as a work item in mlxsw_sp_router_fib_event()
> and scheduled for deferred execution. I am unsure if the execution context of
> this work item is protected by any table lock or rcu_read_lock/rcu_read_unlock
> pair, so I have added the protection. Please let me know if this is redundant.
>
> * Other review comments addressed
>
> v2 -> v3:
> * Removed redundant rcu_read_lock()/rcu_read_unlock() pairs
> * Revised the test script based on Ido Schimmel's feedback
> * Updated the test script to ensure compatibility with the latest iperf3 version
> * Fixed new warnings generated with 'C=2' in the previous version
> * Other review comments addressed
>
> v1 -> v2:
> * list_del_rcu() is applied exclusively to legacy multipath code
> * All occurrences of fib6_siblings have been modified to utilize RCU
> APIs for annotation and usage.
> * Additionally, a test script for reproducing the reported
> issue is included
> ---
> net/ipv6/ip6_fib.c | 8 +-
> net/ipv6/route.c | 45 ++-
> tools/testing/selftests/net/Makefile | 1 +
> .../net/ipv6_route_update_soft_lockup.sh | 262 ++++++++++++++++++
> 4 files changed, 297 insertions(+), 19 deletions(-)
> create mode 100755 tools/testing/selftests/net/ipv6_route_update_soft_lockup.sh
>
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
