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SubjectRe: [PATCH] ipv4: fix a RCU-list lock in fib_triestat_seq_show
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On 3/25/20 10:34 AM, Qian Cai wrote:
>
>
>> On Mar 25, 2020, at 12:13 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
>>
>> I would prefer :
>>
>> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
>> index ff0c24371e3309b3068980f46d1ed743337d2a3e..4b98ffb27136d3b43f179d6b1b42fe84586acc06 100644
>> --- a/net/ipv4/fib_trie.c
>> +++ b/net/ipv4/fib_trie.c
>> @@ -2581,6 +2581,7 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
>> struct hlist_head *head = &net->ipv4.fib_table_hash[h];
>> struct fib_table *tb;
>>
>> + rcu_read_lock();
>> hlist_for_each_entry_rcu(tb, head, tb_hlist) {
>> struct trie *t = (struct trie *) tb->tb_data;
>> struct trie_stat stat;
>> @@ -2596,6 +2597,7 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
>> trie_show_usage(seq, t->stats);
>> #endif
>> }
>> + rcu_read_unlock();
>> }
>>
>> return 0;
>
> I have no strong opinion either way. My initial thought was to save 255 extra lock/unlock with a single lock/unlock, but I am not sure how time-consuming for each iteration of the outer loop could be. If it could take a bit too long, it does make a lot of sense to reduce the critical section.
>


This file could be quite big in some setups.

Alternatively you could use cond_resched_rcu()

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