Re: [PATCH net v2] ip6mr: Fix lockdep and sparse RCU warnings
From: Stefan Wiehler
Date: Tue Oct 01 2024 - 08:50:57 EST
> OK, but RT6_TABLE_DFLT always exists, ip6mr_get_table(net, RT6_TABLE_DFLT)
> can never fail.
>
> This is ensured at netns creation, from ip6mr_rules_init()
OK, but nevertheless we need to enter a RCU read-side critical section before
ip6mr_get_table() is called.
> This complex patch adds some code churn, with no clear bug fix ?
We should have probably mentioned the Lockdep-RCU splat that brought this topic
up:
[ 48.834645] WARNING: suspicious RCU usage
[ 48.834647] 6.1.103-584209f6d5-nokia_sm_x86 #1 Tainted: G S O
[ 48.834649] -----------------------------
[ 48.834651] /net/ipv6/ip6mr.c:132 RCU-list traversed in non-reader section!!
[ 48.834654]
other info that might help us debug this:
[ 48.834656]
rcu_scheduler_active = 2, debug_locks = 1
[ 48.834658] no locks held by radvd/5777.
[ 48.834660]
stack backtrace:
[ 48.834663] CPU: 0 PID: 5777 Comm: radvd Tainted: G S O 6.1.103-584209f6d5-nokia_sm_x86 #1
[ 48.834666] Hardware name: Nokia Asil/Default string, BIOS 0ACNA113 06/07/2024
[ 48.834673] Call Trace:
[ 48.834674] <TASK>
[ 48.834677] dump_stack_lvl+0xb7/0xe9
[ 48.834687] lockdep_rcu_suspicious.cold+0x2d/0x64
[ 48.834697] ip6mr_get_table+0x9f/0xb0
[ 48.834704] ip6mr_ioctl+0x50/0x360
[ 48.834713] ? sk_ioctl+0x5f/0x1c0
[ 48.834719] sk_ioctl+0x5f/0x1c0
[ 48.834723] ? find_held_lock+0x2b/0x80
[ 48.834731] sock_do_ioctl+0x7b/0x140
[ 48.834737] ? proc_nr_files+0x30/0x30
[ 48.834744] sock_ioctl+0x1f5/0x360
[ 48.834754] __x64_sys_ioctl+0x8d/0xd0
[ 48.834760] do_syscall_64+0x3c/0x90
[ 48.834765] entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[ 48.834769] RIP: 0033:0x7fda5f56e2ac
[ 48.834773] Code: 1e fa 48 8d 44 24 08 48 89 54 24 e0 48 89 44 24 c0 48 8d 44 24 d0 48 89 44 24 c8 b8 1 0 00 00 00 c7 44 24 b8 10 00 00 00 0f 05 <3d> 00 f0 ff ff 89 c2 77 0b 89 d0 c3 0f 1f 84 00 00 00 00 00 48 8b
[ 48.834776] RSP: 002b:00007fff52d4bda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[ 48.834782] RAX: ffffffffffffffda RBX: 000000000171cd80 RCX: 00007fda5f56e2ac
[ 48.834784] RDX: 00007fff52d4bdb0 RSI: 0000000000008913 RDI: 0000000000000003
[ 48.834787] RBP: 000000000171cd30 R08: 0000000000000007 R09: 000000000000003c
[ 48.834789] R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000000003
[ 48.834791] R13: 0000000000000000 R14: 0000000000000004 R15: 000000000040d43c
[ 48.834802] </TASK>
Kind regards,
Stefan