Lockdep found the following potential deadlock between mcast_lock and
n_mcast_grps_lock: mcast_lock is taken from both interrupt context and
process context, so spin_lock_irqsave() must be used to take it.
n_mcast_grps_lock is only taken from process context, so at first it
seems safe to take it with plain spin_lock(); however, it also nests
inside mcast_lock, and hence we could deadlock:
cpu A cpu B
ipath_mcast_add():
spin_lock_irq(&mcast_lock);
ipath_mcast_detach():
spin_lock(&n_mcast_grps_lock);
<enter interrupt>
ipath_mcast_find():
spin_lock_irqsave(&mcast_lock);
spin_lock(&n_mcast_grps_lock);
Fix this by using spin_lock_irq() to take n_mcast_grps_lock.
Signed-off-by: Roland Dreier <rolandd@cisco.com>
8b8c8bca3a