[ipset,nf-next] netfilter: ipset: add resched points during set listing

When sets are extremely large we can get softlockup during ipset -L.
We could fix this by adding cond_resched_rcu() at the right location
during iteration, but this only works if RCU nesting depth is 1.

At this time entire variant->list() is called under under rcu_read_lock_bh.
This used to be a read_lock_bh() but as rcu doesn't really lock anything,
it does not appear to be needed, so remove it (ipset increments set
reference count before this, so a set deletion should not be possible).

Reported-by: Li Shuang <shuali@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/ipset/ip_set_bitmap_gen.h | 1 +
 net/netfilter/ipset/ip_set_core.c       | 2 --
 net/netfilter/ipset/ip_set_hash_gen.h   | 1 +
 3 files changed, 2 insertions(+), 2 deletions(-)

Hi Florian,

On Thu, 30 Nov 2017, Florian Westphal wrote:

> When sets are extremely large we can get softlockup during ipset -L. We 
> could fix this by adding cond_resched_rcu() at the right location during 
> iteration, but this only works if RCU nesting depth is 1.
> 
> At this time entire variant->list() is called under under 
> rcu_read_lock_bh. This used to be a read_lock_bh() but as rcu doesn't 
> really lock anything, it does not appear to be needed, so remove it 
> (ipset increments set reference count before this, so a set deletion 
> should not be possible).

Yes, the call of rcu_read_lock_bh() seems to be unnecessary, the
set->variant->list() functions protect the sensitive parts with 
rcu_read_lock() anyway. Thanks!

Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>

Best regards,
Jozsef
 
> Reported-by: Li Shuang <shuali@redhat.com>
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  net/netfilter/ipset/ip_set_bitmap_gen.h | 1 +
>  net/netfilter/ipset/ip_set_core.c       | 2 --
>  net/netfilter/ipset/ip_set_hash_gen.h   | 1 +
>  3 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/netfilter/ipset/ip_set_bitmap_gen.h b/net/netfilter/ipset/ip_set_bitmap_gen.h
> index 5ca18f07683b5..8afe882f846d5 100644
> --- a/net/netfilter/ipset/ip_set_bitmap_gen.h
> +++ b/net/netfilter/ipset/ip_set_bitmap_gen.h
> @@ -227,6 +227,7 @@ mtype_list(const struct ip_set *set,
>  	rcu_read_lock();
>  	for (; cb->args[IPSET_CB_ARG0] < map->elements;
>  	     cb->args[IPSET_CB_ARG0]++) {
> +		cond_resched_rcu();
>  		id = cb->args[IPSET_CB_ARG0];
>  		x = get_ext(set, map, id);
>  		if (!test_bit(id, map->members) ||
> diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
> index 1f3c03b3bebf2..89b44458a7613 100644
> --- a/net/netfilter/ipset/ip_set_core.c
> +++ b/net/netfilter/ipset/ip_set_core.c
> @@ -1388,9 +1388,7 @@ ip_set_dump_start(struct sk_buff *skb, struct netlink_callback *cb)
>  				set->variant->uref(set, cb, true);
>  			/* fall through */
>  		default:
> -			rcu_read_lock_bh();
>  			ret = set->variant->list(set, skb, cb);
> -			rcu_read_unlock_bh();
>  			if (!cb->args[IPSET_CB_ARG0])
>  				/* Set is done, proceed with next one */
>  				goto next_set;
> diff --git a/net/netfilter/ipset/ip_set_hash_gen.h b/net/netfilter/ipset/ip_set_hash_gen.h
> index efffc8eabafea..8ef079db7d347 100644
> --- a/net/netfilter/ipset/ip_set_hash_gen.h
> +++ b/net/netfilter/ipset/ip_set_hash_gen.h
> @@ -1143,6 +1143,7 @@ mtype_list(const struct ip_set *set,
>  	rcu_read_lock();
>  	for (; cb->args[IPSET_CB_ARG0] < jhash_size(t->htable_bits);
>  	     cb->args[IPSET_CB_ARG0]++) {
> +		cond_resched_rcu();
>  		incomplete = skb_tail_pointer(skb);
>  		n = rcu_dereference(hbucket(t, cb->args[IPSET_CB_ARG0]));
>  		pr_debug("cb->arg bucket: %lu, t %p n %p\n",
> -- 
> 2.14.3
> 
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-
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On Fri, Dec 01, 2017 at 08:25:55PM +0100, Jozsef Kadlecsik wrote:
> Hi Florian,
> 
> On Thu, 30 Nov 2017, Florian Westphal wrote:
> 
> > When sets are extremely large we can get softlockup during ipset -L. We 
> > could fix this by adding cond_resched_rcu() at the right location during 
> > iteration, but this only works if RCU nesting depth is 1.
> > 
> > At this time entire variant->list() is called under under 
> > rcu_read_lock_bh. This used to be a read_lock_bh() but as rcu doesn't 
> > really lock anything, it does not appear to be needed, so remove it 
> > (ipset increments set reference count before this, so a set deletion 
> > should not be possible).
> 
> Yes, the call of rcu_read_lock_bh() seems to be unnecessary, the
> set->variant->list() functions protect the sensitive parts with 
> rcu_read_lock() anyway. Thanks!
> 
> Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>

Also applied, thanks.
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