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    Subject[PATCH] net/lockdep: Make nl_table_lock read acquire softirq safe.
    On Wed, Mar 12, 2008 at 01:09:22PM +0100, Peter Zijlstra wrote:
    > =========================================================
    > [ INFO: possible irq lock inversion dependency detected ]
    > 2.6.25-rc4-sched-devel.git #56
    > ---------------------------------------------------------
    > swapper/0 just changed the state of lock:
    > (&rt_hash_locks[i]){-+..}, at: [<ffffffff804721ac>] rt_intern_hash+0x8c/0x3b0
    > but this lock took another, soft-read-irq-unsafe lock in the past:
    > (fib_hash_lock){-.-?}
    >
    > and interrupts could create inverse lock ordering between them.
    >
    >

    I found one more of these during the bootup.

    It appears as though rwlocks totally missed lockdep validation because
    of jumping their dependency chains!

    -->

    From: Gautham R Shenoy <ego@in.ibm.com>

    net: Make nl_table_lock read acquire softirq safe.

    =========================================================
    [ INFO: possible irq lock inversion dependency detected ]
    2.6.25-rc3 #61
    ---------------------------------------------------------
    swapper/0 just changed the state of lock:
    (&tb->tb6_lock){-+..}, at: [<c049a5ab>] __ip6_ins_rt+0x1e/0x3c
    but this lock took another, soft-read-irq-unsafe lock in the past:
    (nl_table_lock){..-?}

    and interrupts could create inverse lock ordering between them.

    Full lockdep report at
    http://gautham.shenoy.googlepages.com/nl_table_lock_irq_inversion.log

    This patch fixes the problem by making the read acquire of nl_table_lock
    softirq safe.

    Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
    Cc: Peter Ziljstra <a.p.zijlstra@chello.nl>
    Cc: Eric Dumazet <dada1@cosmosbay.com>
    Cc: David S. Miller <davem@davemloft.net>

    diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
    index 1ab0da2..7ade317 100644
    --- a/net/netlink/af_netlink.c
    +++ b/net/netlink/af_netlink.c
    @@ -205,9 +205,9 @@ netlink_lock_table(void)
    {
    /* read_lock() synchronizes us to netlink_table_grab */

    - read_lock(&nl_table_lock);
    + read_lock_bh(&nl_table_lock);
    atomic_inc(&nl_table_users);
    - read_unlock(&nl_table_lock);
    + read_unlock_bh(&nl_table_lock);
    }

    static inline void
    @@ -225,7 +225,7 @@ static inline struct sock *netlink_lookup(struct net *net, int protocol,
    struct sock *sk;
    struct hlist_node *node;

    - read_lock(&nl_table_lock);
    + read_lock_bh(&nl_table_lock);
    head = nl_pid_hashfn(hash, pid);
    sk_for_each(sk, node, head) {
    if ((sk->sk_net == net) && (nlk_sk(sk)->pid == pid)) {
    @@ -235,7 +235,7 @@ static inline struct sock *netlink_lookup(struct net *net, int protocol,
    }
    sk = NULL;
    found:
    - read_unlock(&nl_table_lock);
    + read_unlock_bh(&nl_table_lock);
    return sk;
    }

    @@ -1078,12 +1078,12 @@ void netlink_set_err(struct sock *ssk, u32 pid, u32 group, int code)
    info.group = group;
    info.code = code;

    - read_lock(&nl_table_lock);
    + read_lock_bh(&nl_table_lock);

    sk_for_each_bound(sk, node, &nl_table[ssk->sk_protocol].mc_list)
    do_one_set_err(sk, &info);

    - read_unlock(&nl_table_lock);
    + read_unlock_bh(&nl_table_lock);
    }

    /* must be called with netlink table grabbed */
    @@ -1776,7 +1776,7 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
    static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
    __acquires(nl_table_lock)
    {
    - read_lock(&nl_table_lock);
    + read_lock_bh(&nl_table_lock);
    return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
    }

    @@ -1825,7 +1825,7 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
    static void netlink_seq_stop(struct seq_file *seq, void *v)
    __releases(nl_table_lock)
    {
    - read_unlock(&nl_table_lock);
    + read_unlock_bh(&nl_table_lock);
    }


    --
    Thanks and Regards
    gautham

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