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    Subjectrcu read-side protection
    Date
    In dn_neigh_construct() of linux-2.6.12/net/decnet/dn_neigh.c

    static int dn_neigh_construct(struct neighbour *neigh)
    {
    struct net_device *dev = neigh->dev;
    struct dn_neigh *dn = (struct dn_neigh *)neigh;
    struct dn_dev *dn_db;
    struct neigh_parms *parms;

    rcu_read_lock();
    dn_db = rcu_dereference(dev->dn_ptr);
    if (dn_db == NULL) {
    rcu_read_unlock();
    return -EINVAL;
    }

    parms = dn_db->neigh_parms;
    if (!parms) {
    rcu_read_unlock();
    return -EINVAL;
    }

    __neigh_parms_put(neigh->parms);
    neigh->parms = neigh_parms_clone(parms);
    rcu_read_unlock();

    if (dn_db->use_long)
    neigh->ops = &dn_long_ops;
    else
    neigh->ops = &dn_short_ops;

    if (dn->flags & DN_NDFLAG_P3)
    neigh->ops = &dn_phase3_ops;

    neigh->nud_state = NUD_NOARP;
    neigh->output = neigh->ops->connected_output;

    if ((dev->type == ARPHRD_IPGRE) || (dev->flags & IFF_POINTOPOINT))
    memcpy(neigh->ha, dev->broadcast, dev->addr_len);
    else if ((dev->type == ARPHRD_ETHER) || (dev->type == ARPHRD_LOOPBACK))
    dn_dn2eth(neigh->ha, dn->addr);
    else {
    if (net_ratelimit())
    printk(KERN_DEBUG "Trying to create neigh for hw %d\n", dev->type);
    return -EINVAL;
    }

    A read-side critical section is marked to protect the dereference of the
    dn_ptr and assignment to dn_db which is a pointer to a dn_dev. (struct
    net_device is defined in /linux/netdevice.h and its dn_ptr in
    /include/net/dn_dev.h) Should this rcu-protection be extended to the line
    following rcu_read_lock()? Even though use_long is a simple char, it
    appears to be a member of an rcu-protected structure.

    Thank you.


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