[PATCH] xen/domain: Fix label position in domain_teardown()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

As explained in the comments, a progress label wants to be before the function
it refers to for the higher level logic to make sense.  As it happens, the
effects are benign because gnttab_mappings is immediately adjacent to teardown
in terms of co-routine exit points.

There is and will always be a corner case with 0.  Help alleviate this
visually (at least slightly) with a BUILD_BUG_ON() to ensure the property
which makes this function do anything useful.

There is also a visual corner case when changing from PROGRESS() to
PROGRESS_VCPU().  The important detail is to check that there is a "return
rc;" logically between each PROGRESS*() marker.

Fixes: b1ee10be5625 ("gnttab: add preemption check to 
gnttab_release_mappings()")
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 xen/common/domain.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 14b1341e53c6..0d3385ad5a66 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -419,11 +419,13 @@ static int domain_teardown(struct domain *d)
         };
 
     case PROG_none:
+        BUILD_BUG_ON(PROG_none != 0);
+
+    PROGRESS(gnttab_mappings):
         rc = gnttab_release_mappings(d);
         if ( rc )
             return rc;
 
-    PROGRESS(gnttab_mappings):
         for_each_vcpu ( d, v )
         {
             PROGRESS_VCPU(teardown);
-- 
2.11.0