Messages in this thread |  | | | Date | Wed, 17 Jun 2009 14:36:14 +0200 | | From | Patrick McHardy <> | | Subject | Re: [bug] __nf_ct_refresh_acct(): WARNING: at lib/list_debug.c:30 __list_add+0x7d/0xad() |
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Eric Dumazet wrote: > Patrick McHardy a écrit : >> Eric Dumazet wrote: >>> Patrick McHardy a écrit : >>>> Before the conntrack is confirmed, it is exclusively handled by a >>>> single CPU. I agree that we need to make sure the IPS_CONFIRMED_BIT >>>> is visible before we add the conntrack to the hash table since the >>>> lookup is lockless, but simply moving the set_bit before the hash >>>> insertion should be fine I think. >>>> >>> >>> Problem is timeout.expires is either a relative or absolute timeout, >>> and changes happen >>> in __nf_conntrack_confirm() or __nf_ct_refresh_acct(). >>> >>> We must have a synchronization (an barriers), a single bit wont be >>> enough. >> Please have a look at the second patch I just sent. It relies >> on the RCU barriers to make sure all stores are visible before >> other CPUs can find the conntrack. >> > > Sorry, I dont understand how your second patch corrects the problem. > > This (unconfirmed) conntrack is visible by another cpu.
No, before it is confirmed, its only visible to the CPU handling the initial packet of a connection. Confirmation is the step that makes it visible to other CPUs.
> This other > cpu can call __nf_ct_refresh_acct() while this cpu runs > in __nf_conntrack_confirm()
Not for the same conntrack, that would be a seperate bug.
Does that explain what I'm trying to do? :)
> > @@ -425,7 +425,6 @@ __nf_conntrack_confirm(struct sk_buff *skb) > /* Remove from unconfirmed list */ > hlist_nulls_del_rcu(&ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode); > > - __nf_conntrack_hash_insert(ct, hash, repl_hash); > /* Timer relative to confirmation time, not original > setting time, otherwise we'd get timer wrap in > weird delay cases. */ > @@ -433,8 +432,15 @@ __nf_conntrack_confirm(struct sk_buff *skb) > add_timer(&ct->timeout); > > <<<< another cpu could here change timeout.expires (thinking its still relative) >>>> > > atomic_inc(&ct->ct_general.use); > set_bit(IPS_CONFIRMED_BIT, &ct->status); > + > + /* Since the lookup is lockless, hash insertion must be after starting the > + * timer and setting the CONFIRMED bit. The RCU barriers guarantee that no > + * other CPU can find the conntrack before the above stores are visible. > + */ > + __nf_conntrack_hash_insert(ct, hash, repl_hash); > NF_CT_STAT_INC(net, insert); > spin_unlock_bh(&nf_conntrack_lock); > help = nfct_help(ct); > if (help && help->helper) > nf_conntrack_event_cache(IPCT_HELPER, ct); >
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