On Thu, 2 Apr 2009 22:12:45 +0200 Ingo Molnar <mingo@xxxxxxx> wrote: > > Impact: fix log spam under CONFIG_DEBUG_PREEMPT=y > > This recent commit: > > 7845447: netfilter: iptables: lock free counters > > Converted a couple of netfilter codepaths from read_lock() critical > sections to lockless rcu_read_lock(). What it forgot about is that > under CONFIG_PREEMPT=y and CONFIG_PREEMPT_RCU=y these sections can > be preempted. > > Under CONFIG_DEBUG_PREEMPT=y this produces such warnings: > > BUG: using smp_processor_id() in preemptible [00000000] code: ssh/9115 > caller is ipt_do_table+0xc8/0x559 > Pid: 9115, comm: ssh Tainted: G W 2.6.29-tip-08646-g45ef7c3-dirty #26231 > Call Trace: > [<c0c0dacf>] ? printk+0x14/0x16 > [<c048c2e6>] debug_smp_processor_id+0xa6/0xbc > [<c0adbd03>] ipt_do_table+0xc8/0x559 > [<c0c10277>] ? _read_unlock+0x3d/0x49 > [<c0ad68c0>] ? fn_hash_lookup+0x94/0xa0 > [<c0ad330e>] ? __inet_dev_addr_type+0x56/0x8d > [<c0a87b02>] ? neigh_lookup+0xe5/0x108 > [<c0adc2bc>] ipt_local_hook+0x40/0x50 > [<c0a93e57>] nf_iterate+0x34/0x80 > [<c0aad4b8>] ? dst_output+0x0/0x10 > [<c0a93eea>] nf_hook_slow+0x47/0xa4 > [<c0aad4b8>] ? dst_output+0x0/0x10 > [<c0aaec04>] __ip_local_out+0x78/0x7f > [<c0aad4b8>] ? dst_output+0x0/0x10 > [<c0aaec1b>] ip_local_out+0x10/0x20 > [<c0aaf416>] ip_queue_xmit+0x2bc/0x332 > [<c0aa8fdf>] ? __ip_route_output_key+0x112/0x77b > [<c01397fe>] ? local_bh_enable+0x10/0x12 > [<c0abf0e5>] ? tcp_connect+0x32a/0x3bb > [<c0ab15a7>] ? __inet_hash_nolisten+0x97/0xaf > [<c0a78dde>] ? __copy_skb_header+0xe/0x13a > [<c0abf0e5>] ? tcp_connect+0x32a/0x3bb > [<c0abe955>] ? tcp_transmit_skb+0x5a5/0x61c > [<c0abe995>] tcp_transmit_skb+0x5e5/0x61c > [<c0a7b6c0>] ? __alloc_skb+0x54/0x120 > [<c0abefca>] ? tcp_connect+0x20f/0x3bb > [<c0abf0e5>] tcp_connect+0x32a/0x3bb > [<c0ac4b68>] tcp_v4_connect+0x466/0x4be > [<c0acf380>] inet_stream_connect+0x8f/0x212 > [<c018f4e6>] ? might_fault+0x75/0x77 > [<c047f198>] ? copy_from_user+0x2f/0x117 > BUG: using smp_processor_id() in preemptible [00000000] code: ssh/9114 > > Since it appears that the tables are RCU freed, and there are no > non-preempt assumptions in the code, the using of > raw_smp_processor_id() is safe. > > [ I also audited all of net/netfilter/*.c for smp_processor_id() use, > and fixed all places that used them unsafely. ] > > Signed-off-by: Ingo Molnar <mingo@xxxxxxx> > --- > net/ipv4/netfilter/arp_tables.c | 2 +- > net/ipv4/netfilter/ip_tables.c | 4 ++-- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c > index 35c5f6a..30baf3e 100644 > --- a/net/ipv4/netfilter/arp_tables.c > +++ b/net/ipv4/netfilter/arp_tables.c > @@ -255,7 +255,7 @@ unsigned int arpt_do_table(struct sk_buff *skb, > > rcu_read_lock(); > private = rcu_dereference(table->private); > - table_base = rcu_dereference(private->entries[smp_processor_id()]); > + table_base = rcu_dereference(private->entries[raw_smp_processor_id()]); > > e = get_entry(table_base, private->hook_entry[hook]); > back = get_entry(table_base, private->underflow[hook]); > diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c > index 82ee7c9..eff124e 100644 > --- a/net/ipv4/netfilter/ip_tables.c > +++ b/net/ipv4/netfilter/ip_tables.c > @@ -280,7 +280,7 @@ static void trace_packet(struct sk_buff *skb, > char *hookname, *chainname, *comment; > unsigned int rulenum = 0; > > - table_base = (void *)private->entries[smp_processor_id()]; > + table_base = (void *)private->entries[raw_smp_processor_id()]; > root = get_entry(table_base, private->hook_entry[hook]); > > hookname = chainname = (char *)hooknames[hook]; > @@ -341,7 +341,7 @@ ipt_do_table(struct sk_buff *skb, > > rcu_read_lock(); > private = rcu_dereference(table->private); > - table_base = rcu_dereference(private->entries[smp_processor_id()]); > + table_base = rcu_dereference(private->entries[raw_smp_processor_id()]); > > e = get_entry(table_base, private->hook_entry[hook]); > NAK. The rcu_read_lock() needs to be rcu_read_lock_bh() otherwise RCU could corrupt the referenceses. -- To unsubscribe from this list: send the line "unsubscribe netfilter" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
