From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [GIT] Networking Date: Sun, 15 Aug 2010 16:47:17 +0200 Message-ID: <1281883637.2942.42.camel@edumazet-laptop> References: <20100812.161050.246523792.davem@davemloft.net> <20100814.220945.232761341.davem@davemloft.net> <1281869722.2942.20.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Patrick McHardy To: David Miller Return-path: In-Reply-To: <1281869722.2942.20.camel@edumazet-laptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Le dimanche 15 ao=C3=BBt 2010 =C3=A0 12:55 +0200, Eric Dumazet a =C3=A9= crit : > We have one lock per cpu, and only one cpu can possibly lock its > associated lock under softirq. So the usual lockdep check, warning a > lock is taken with BH enabled, while same lock was taken inside softi= rq > handler is triggering a false positive here. >=20 > I believe no existing lockdep annotation can instruct lockdep this us= e > is OK, I guess we have following choice : >=20 > 1) Mask BH again, using xt_info_wrlock_lockdep(cpu) instead of > xt_info_wrlock(cpu). >=20 > xt_info_wrlock_lockdep() being a variant, that disables BH in case > CONFIG_PROVE_LOCKING=3Dy >=20 > 2) temporally switch off lockdep in get_counters(), using a > lockdep_off()/lockdep_on() pair, and a comment why this is necessary. >=20 In any case, here is patch implementing the later CC Patrick, our netfilter maintainer... Maybe lockdep rules could be improved to take care of this later ? Thanks [PATCH] netfilter: {ip,ip6,arp}_tables: avoid lockdep false positive After commit 24b36f019 (netfilter: {ip,ip6,arp}_tables: dont block bottom half more than necessary), lockdep can raise a warning because we attempt to lock a spinlock with BH enabled, while the same lock is usually locked by another cpu in a softirq context. In this use case, the lockdep splat is a false positive, because the BH disabling only matters for one cpu for a given lock (we use one lock per cpu). Use lockdep_off()/lockdep_on() around the problematic section to avoid the splat. Reported-by: Linus Torvalds Diagnosed-by: David S. Miller Signed-off-by: Eric Dumazet CC: Patrick McHardy --- net/ipv4/netfilter/arp_tables.c | 3 +++ net/ipv4/netfilter/ip_tables.c | 3 +++ net/ipv6/netfilter/ip6_tables.c | 3 +++ 3 files changed, 9 insertions(+) diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_t= ables.c index 6bccba3..b4f7ebf 100644 --- a/net/ipv4/netfilter/arp_tables.c +++ b/net/ipv4/netfilter/arp_tables.c @@ -729,8 +729,10 @@ static void get_counters(const struct xt_table_inf= o *t, local_bh_enable(); /* Processing counters from other cpus, we can let bottom half enable= d, * (preemption is disabled) + * We must turn off lockdep to avoid a false positive. */ =20 + lockdep_off(); for_each_possible_cpu(cpu) { if (cpu =3D=3D curcpu) continue; @@ -743,6 +745,7 @@ static void get_counters(const struct xt_table_info= *t, } xt_info_wrunlock(cpu); } + lockdep_on(); put_cpu(); } =20 diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tab= les.c index c439721..dc5b2fd 100644 --- a/net/ipv4/netfilter/ip_tables.c +++ b/net/ipv4/netfilter/ip_tables.c @@ -903,8 +903,10 @@ get_counters(const struct xt_table_info *t, local_bh_enable(); /* Processing counters from other cpus, we can let bottom half enable= d, * (preemption is disabled) + * We must turn off lockdep to avoid a false positive. */ =20 + lockdep_off(); for_each_possible_cpu(cpu) { if (cpu =3D=3D curcpu) continue; @@ -917,6 +919,7 @@ get_counters(const struct xt_table_info *t, } xt_info_wrunlock(cpu); } + lockdep_on(); put_cpu(); } =20 diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_t= ables.c index 5359ef4..fb55443 100644 --- a/net/ipv6/netfilter/ip6_tables.c +++ b/net/ipv6/netfilter/ip6_tables.c @@ -916,8 +916,10 @@ get_counters(const struct xt_table_info *t, local_bh_enable(); /* Processing counters from other cpus, we can let bottom half enable= d, * (preemption is disabled) + * We must turn off lockdep to avoid a false positive. */ =20 + lockdep_off(); for_each_possible_cpu(cpu) { if (cpu =3D=3D curcpu) continue; @@ -930,6 +932,7 @@ get_counters(const struct xt_table_info *t, } xt_info_wrunlock(cpu); } + lockdep_on(); put_cpu(); } =20