tmem: add matching unlock for an about-to-be-destroyed object

A 4.2 changeset forces a preempt_disable/enable with
every lock/unlock.

Tmem has dynamically allocated "objects" that contain a
lock.  The lock is held when the object is destroyed.
No reason to unlock something that's about to be destroyed!
But with the preempt_enable/disable in the generic locking code,
and the fact that do_softirq ASSERTs that preempt_count
must be zero, a crash occurs soon after any object is
destroyed.

So force lock to be released before destroying objects.

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Committed-by: Keir Fraser <keir@xen.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/xen/common/tmem.c b/xen/common/tmem.c
index dd276df327..1a8777c284 100644
--- a/xen/common/tmem.c
+++ b/xen/common/tmem.c
@@ -952,6 +952,7 @@ static NOINLINE void obj_free(obj_t *obj, int no_rebalance)
     /* use no_rebalance only if all objects are being destroyed anyway */
     if ( !no_rebalance )
         rb_erase(&obj->rb_tree_node,&pool->obj_rb_root[oid_hash(&old_oid)]);
+    tmem_spin_unlock(&obj->obj_spinlock);
     tmem_free(obj,sizeof(obj_t),pool);
 }