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    SubjectRe: [GIT] Networking
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    Le dimanche 15 août 2010 à 12:55 +0200, Eric Dumazet a écrit :

    > 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 softirq
    > handler is triggering a false positive here.
    >
    > I believe no existing lockdep annotation can instruct lockdep this use
    > is OK, I guess we have following choice :
    >
    > 1) Mask BH again, using xt_info_wrlock_lockdep(cpu) instead of
    > xt_info_wrlock(cpu).
    >
    > xt_info_wrlock_lockdep() being a variant, that disables BH in case
    > CONFIG_PROVE_LOCKING=y
    >
    > 2) temporally switch off lockdep in get_counters(), using a
    > lockdep_off()/lockdep_on() pair, and a comment why this is necessary.
    >

    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 <torvalds@linux-foundation.org>
    Diagnosed-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
    CC: Patrick McHardy <kaber@trash.net>
    ---
    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_tables.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_info *t,
    local_bh_enable();
    /* Processing counters from other cpus, we can let bottom half enabled,
    * (preemption is disabled)
    + * We must turn off lockdep to avoid a false positive.
    */

    + lockdep_off();
    for_each_possible_cpu(cpu) {
    if (cpu == curcpu)
    continue;
    @@ -743,6 +745,7 @@ static void get_counters(const struct xt_table_info *t,
    }
    xt_info_wrunlock(cpu);
    }
    + lockdep_on();
    put_cpu();
    }

    diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.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 enabled,
    * (preemption is disabled)
    + * We must turn off lockdep to avoid a false positive.
    */

    + lockdep_off();
    for_each_possible_cpu(cpu) {
    if (cpu == curcpu)
    continue;
    @@ -917,6 +919,7 @@ get_counters(const struct xt_table_info *t,
    }
    xt_info_wrunlock(cpu);
    }
    + lockdep_on();
    put_cpu();
    }

    diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.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 enabled,
    * (preemption is disabled)
    + * We must turn off lockdep to avoid a false positive.
    */

    + lockdep_off();
    for_each_possible_cpu(cpu) {
    if (cpu == curcpu)
    continue;
    @@ -930,6 +932,7 @@ get_counters(const struct xt_table_info *t,
    }
    xt_info_wrunlock(cpu);
    }
    + lockdep_on();
    put_cpu();
    }


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