[Xen-changelog] [xen-unstable] [XEN] Remove a race condition in shadow mark_dirty code.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
# Date 1172843199 0
# Node ID a69d98bf0c5570f9157a95155f25d62b0ff76608
# Parent  3ac19fda0bc256bac20a4decf7e13bb086162220
[XEN] Remove a race condition in shadow mark_dirty code.
Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
---
 xen/arch/x86/mm/shadow/common.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletion(-)

diff -r 3ac19fda0bc2 -r a69d98bf0c55 xen/arch/x86/mm/shadow/common.c
--- a/xen/arch/x86/mm/shadow/common.c   Fri Mar 02 12:11:52 2007 +0000
+++ b/xen/arch/x86/mm/shadow/common.c   Fri Mar 02 13:46:39 2007 +0000
@@ -2912,7 +2912,16 @@ void sh_mark_dirty(struct domain *d, mfn
      * can be called from __hvm_copy during emulation).
      * If the lock isn't held, take it for the duration of the call. */
     do_locking = !shadow_locked_by_me(d);
-    if ( do_locking ) shadow_lock(d);
+    if ( do_locking ) 
+    { 
+        shadow_lock(d);
+        /* Check the mode again with the lock held */ 
+        if ( unlikely(!shadow_mode_log_dirty(d)) )
+        {
+            shadow_unlock(d);
+            return;
+        }
+    }
 
     ASSERT(d->arch.paging.shadow.dirty_bitmap != NULL);
 

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