[PATCH] rcu in bpqether driver.

[PATCH] rcu in bpqether driver.

From Suzanne Wood <suzannew@cs.pdx.edu>:

Clarify RCU implementation in bpqether.c.

Because bpq_new_device() calls list_add_rcu() and bpq_free_device() calls
list_del_rcu(), substitute list_for_each_entry_rcu() for
list_for_each_entry() in bpq_get_ax25_dev() and in bpq_seq_start().

Add rcu dereference protection in bpq_seq_next().

The rcu_read_lock()/unlock() in bpq_device_event() are removed because
netdev event handlers are called with RTNL locking in place.

FYI: bpq_free_device() calls list_del_rcu() which, per list.h, requires
synchronize_rcu() which can block or call_rcu() or call_rcu_bh() which
cannot block.  Herbert Xu notes that synchronization is done here by
unregister_netdevice().  This calls synchronize_net() which in turn uses
synchronize_rcu().

Signed-off-by: Ralf Baechle DL5RB <ralf@linux-mips.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>