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
Signed-off-by: Qian Cai <[email protected]>
---
net/ipv4/fib_trie.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index ff0c24371e33..73fa37476f03 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -2577,6 +2577,7 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
" %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;
@@ -2597,6 +2598,7 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
#endif
}
}
+ rcu_read_unlock();
return 0;
}
--
2.21.0 (Apple Git-122.2)
On 3/25/20 8:55 AM, Qian Cai wrote:
> 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
>
> Signed-off-by: Qian Cai <[email protected]>
> ---
> net/ipv4/fib_trie.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index ff0c24371e33..73fa37476f03 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -2577,6 +2577,7 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
> " %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;
> @@ -2597,6 +2598,7 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
> #endif
> }
> }
> + rcu_read_unlock();
>
> return 0;
> }
>
We probably want to be able to reschedule in the loop (adding a cond_resched() in net-next)
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;
> On Mar 25, 2020, at 12:13 PM, Eric Dumazet <[email protected]> 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.
On 3/25/20 10:34 AM, Qian Cai wrote:
>
>
>> On Mar 25, 2020, at 12:13 PM, Eric Dumazet <[email protected]> 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()