[Xen-devel] [PATCH] [FOR 4.2] tmem: add matching unlock for an about-to-be-destroyed object

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

(Guidance appreciated if the Xen patch submittal process
has changed and I need to do more than send this email.)

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@xxxxxxxxxx>

diff -r 1967c7c290eb xen/common/tmem.c
--- a/xen/common/tmem.c Wed Feb 09 12:03:09 2011 +0000
+++ b/xen/common/tmem.c Fri Aug 31 13:49:51 2012 -0600
@@ -957,6 +957,7 @@
     /* 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);
 }

Attachment: xen-tmem-destroy-obj.patch
Description: Binary data

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel