[Xen-changelog] [xen-unstable] x86/mm: Take care of domain reference for shared pages

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
# Date 1333620363 -3600
# Node ID d690c7e896a26c54a5ab85458824059de72d5cba
# Parent  80e3ac42e5a1f1974afaff0292b69199dba589cb
x86/mm: Take care of domain reference for shared pages

Making a page sharable removes it from the previous owner's list. Making it
private adds it. These actions are similar to freeing or allocating a page.
Except that they were not minding the domain reference that is taken/dropped
when the first/last page is allocated/freed.

Without fixing this, a domain might remain zombie when destroyed if all its
pages are shared.

Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
Acked-by: Tim Deegan <tim@xxxxxxx>
Committed-by: Tim Deegan <tim@xxxxxxx>
---


diff -r 80e3ac42e5a1 -r d690c7e896a2 xen/arch/x86/mm/mem_sharing.c
--- a/xen/arch/x86/mm/mem_sharing.c     Tue Apr 03 17:22:59 2012 +0200
+++ b/xen/arch/x86/mm/mem_sharing.c     Thu Apr 05 11:06:03 2012 +0100
@@ -401,6 +401,7 @@ static int page_make_sharable(struct dom
                        struct page_info *page, 
                        int expected_refcnt)
 {
+    int drop_dom_ref;
     spin_lock(&d->page_alloc_lock);
 
     /* Change page type and count atomically */
@@ -430,8 +431,12 @@ static int page_make_sharable(struct dom
 
     page_set_owner(page, dom_cow);
     d->tot_pages--;
+    drop_dom_ref = (d->tot_pages == 0);
     page_list_del(page, &d->page_list);
     spin_unlock(&d->page_alloc_lock);
+
+    if ( drop_dom_ref )
+        put_domain(d);
     return 0;
 }
 
@@ -466,7 +471,8 @@ static int page_make_private(struct doma
     ASSERT(page_get_owner(page) == dom_cow);
     page_set_owner(page, d);
 
-    d->tot_pages++;
+    if ( d->tot_pages++ == 0 )
+        get_domain(d);
     page_list_add_tail(page, &d->page_list);
     spin_unlock(&d->page_alloc_lock);
 

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