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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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