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

[patchbot@xxxxxxx]

commit 8064488062641ae505b2a7369611c38057a7788b
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Aug 27 14:46:52 2021 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Aug 27 15:12:05 2021 +0100

    xen/domain: Fix label position in domain_teardown()
    
    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>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 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 14b1341e53..0d3385ad5a 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);
--
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