From: Roland Dreier <rolandd@cisco.com>
Date: Sat, 19 May 2007 15:51:53 +0000 (-0700)
Subject: IB/ipath: Fix potential deadlock with multicast spinlocks
X-Git-Tag: v2.6.22-rc3~108^2~17
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8b8c8bca3a63073bac20f0fca178e00fdf7f5a09;p=pandora-kernel.git

IB/ipath: Fix potential deadlock with multicast spinlocks

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>
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