| From foo@baz Fri 03 Apr 2020 11:04:16 AM CEST |
| From: Qian Cai <cai@lca.pw> |
| Date: Wed, 25 Mar 2020 18:01:00 -0400 |
| Subject: ipv4: fix a RCU-list lock in fib_triestat_seq_show |
| |
| From: Qian Cai <cai@lca.pw> |
| |
| [ Upstream commit fbe4e0c1b298b4665ee6915266c9d6c5b934ef4a ] |
| |
| fib_triestat_seq_show() calls hlist_for_each_entry_rcu(tb, head, |
| tb_hlist) without rcu_read_lock() will trigger a warning, |
| |
| net/ipv4/fib_trie.c:2579 RCU-list traversed in non-reader section!! |
| |
| other info that might help us debug this: |
| |
| rcu_scheduler_active = 2, debug_locks = 1 |
| 1 lock held by proc01/115277: |
| #0: c0000014507acf00 (&p->lock){+.+.}-{3:3}, at: seq_read+0x58/0x670 |
| |
| Call Trace: |
| dump_stack+0xf4/0x164 (unreliable) |
| lockdep_rcu_suspicious+0x140/0x164 |
| fib_triestat_seq_show+0x750/0x880 |
| seq_read+0x1a0/0x670 |
| proc_reg_read+0x10c/0x1b0 |
| __vfs_read+0x3c/0x70 |
| vfs_read+0xac/0x170 |
| ksys_read+0x7c/0x140 |
| system_call+0x5c/0x68 |
| |
| Fix it by adding a pair of rcu_read_lock/unlock() and use |
| cond_resched_rcu() to avoid the situation where walking of a large |
| number of items may prevent scheduling for a long time. |
| |
| Signed-off-by: Qian Cai <cai@lca.pw> |
| Reviewed-by: Eric Dumazet <edumazet@google.com> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| net/ipv4/fib_trie.c | 3 +++ |
| 1 file changed, 3 insertions(+) |
| |
| --- a/net/ipv4/fib_trie.c |
| +++ b/net/ipv4/fib_trie.c |
| @@ -2256,6 +2256,7 @@ static int fib_triestat_seq_show(struct |
| " %Zd bytes, size of tnode: %Zd bytes.\n", |
| LEAF_SIZE, TNODE_SIZE(0)); |
| |
| + rcu_read_lock(); |
| for (h = 0; h < FIB_TABLE_HASHSZ; h++) { |
| struct hlist_head *head = &net->ipv4.fib_table_hash[h]; |
| struct fib_table *tb; |
| @@ -2275,7 +2276,9 @@ static int fib_triestat_seq_show(struct |
| trie_show_usage(seq, t->stats); |
| #endif |
| } |
| + cond_resched_rcu(); |
| } |
| + rcu_read_unlock(); |
| |
| return 0; |
| } |