* [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show
@ 2020-03-25 22:01 Qian Cai
2020-03-27 3:27 ` David Miller
2020-03-30 4:52 ` David Miller
0 siblings, 2 replies; 4+ messages in thread
From: Qian Cai @ 2020-03-25 22:01 UTC (permalink / raw)
To: davem
Cc: kuznet, yoshfuji, kuba, eric.dumazet, netdev, linux-kernel, Qian Cai
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>
---
Use cond_resched_rcu() from Eric.
net/ipv4/fib_trie.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index ff0c24371e33..3be0affbabd3 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;
@@ -2596,7 +2597,9 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
trie_show_usage(seq, t->stats);
#endif
}
+ cond_resched_rcu();
}
+ rcu_read_unlock();
return 0;
}
--
2.21.0 (Apple Git-122.2)
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show
2020-03-25 22:01 [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show Qian Cai
@ 2020-03-27 3:27 ` David Miller
2020-03-27 5:41 ` Eric Dumazet
2020-03-30 4:52 ` David Miller
1 sibling, 1 reply; 4+ messages in thread
From: David Miller @ 2020-03-27 3:27 UTC (permalink / raw)
To: cai; +Cc: kuznet, yoshfuji, kuba, eric.dumazet, netdev, linux-kernel
From: Qian Cai <cai@lca.pw>
Date: Wed, 25 Mar 2020 18:01:00 -0400
> 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>
Eric, please review.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show
2020-03-27 3:27 ` David Miller
@ 2020-03-27 5:41 ` Eric Dumazet
0 siblings, 0 replies; 4+ messages in thread
From: Eric Dumazet @ 2020-03-27 5:41 UTC (permalink / raw)
To: David Miller, cai
Cc: kuznet, yoshfuji, kuba, eric.dumazet, netdev, linux-kernel
On 3/26/20 8:27 PM, David Miller wrote:
> From: Qian Cai <cai@lca.pw>
> Date: Wed, 25 Mar 2020 18:01:00 -0400
>> 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>
>
> Eric, please review.
>
Patch looks good to me, thanks !
Reviewed-by: Eric Dumazet <edumazet@google.com>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show
2020-03-25 22:01 [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show Qian Cai
2020-03-27 3:27 ` David Miller
@ 2020-03-30 4:52 ` David Miller
1 sibling, 0 replies; 4+ messages in thread
From: David Miller @ 2020-03-30 4:52 UTC (permalink / raw)
To: cai; +Cc: kuznet, yoshfuji, kuba, eric.dumazet, netdev, linux-kernel
From: Qian Cai <cai@lca.pw>
Date: Wed, 25 Mar 2020 18:01:00 -0400
> 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>
Applied and queued up for -stable, thanks.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-03-25 22:01 [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show Qian Cai
2020-03-27 3:27 ` David Miller
2020-03-27 5:41 ` Eric Dumazet
2020-03-30 4:52 ` David Miller
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