The loop in fib_table_flush [1] calls trie_firstleaf() which
RCU-dereferences a structure outside a RCU read critical section,
generating a warning [2].
Since trie_leaf_remove() uses rcu_assign_pointer(), which should be
outside the RCU read critical section, is there any better solution
than spitting up the loop, with the first half covered by a RCU read
critical section lock?
Daniel
--- [1]
int fib_table_flush(struct fib_table *tb)
{
struct trie *t = (struct trie *) tb->tb_data;
struct leaf *l, *ll = NULL;
int found = 0;
for (l = trie_firstleaf(t); l; l = trie_nextleaf(l)) {
found += trie_flush_leaf(l);
if (ll && hlist_empty(&ll->list))
trie_leaf_remove(t, ll);
ll = l;
}
--- [2]
===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
net/ipv4/fib_trie.c:1777 invoked rcu_dereference_check() without protection!
other info that might help us debug this:
rcu_scheduler_active = 1, debug_locks = 1
3 locks held by kworker/u:5/51:
#0: (netns){.+.+.+}, at: [<ffffffff8107b639>] process_one_work+0x149/0x470
#1: (net_cleanup_work){+.+.+.}, at: [<ffffffff8107b639>]
process_one_work+0x149/0x470
#2: (net_mutex){+.+.+.}, at: [<ffffffff8157b4b0>] cleanup_net+0x80/0x1b0
stack backtrace:
Pid: 51, comm: kworker/u:5 Tainted: G W 2.6.39-rc1-350cd #1
Call Trace:
[<ffffffff81094cd4>] lockdep_rcu_dereference+0xa4/0xc0
[<ffffffff8160aa23>] trie_firstleaf+0x93/0xa0
[<ffffffff8156feb8>] ? __sk_free+0x148/0x1e0
[<ffffffff8160d890>] fib_table_flush+0x20/0x1a0
[<ffffffff81606da5>] ip_fib_net_exit+0x95/0xd0
[<ffffffff81606e10>] fib_net_exit+0x30/0x40
[<ffffffff8157ab8e>] ops_exit_list+0x2e/0x70
[<ffffffff8157b52b>] cleanup_net+0xfb/0x1b0
[<ffffffff8107b69a>] process_one_work+0x1aa/0x470
[<ffffffff8107b639>] ? process_one_work+0x149/0x470
[<ffffffff8157b430>] ? net_free+0x30/0x30
[<ffffffff8107bd97>] worker_thread+0x157/0x3c0
[<ffffffff816ea484>] ? preempt_schedule+0x44/0x60
[<ffffffff8107bc40>] ? rescuer_thread+0x2e0/0x2e0
[<ffffffff81080236>] kthread+0xb6/0xc0
[<ffffffff81095f1d>] ? trace_hardirqs_on_caller+0x14d/0x190
[<ffffffff816ef094>] kernel_thread_helper+0x4/0x10
[<ffffffff810553f8>] ? finish_task_switch+0x78/0x110
[<ffffffff816ed7c4>] ? retint_restore_args+0xe/0xe
[<ffffffff81080180>] ? __init_kthread_worker+0x70/0x70
[<ffffffff816ef090>] ? gs_change+0xb/0xb
--
Daniel J Blueman
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