[Xen-changelog] [xen staging] x86/mm: drop redundant smp_wmb() from _put_final_page_type()

[patchbot@xxxxxxx]

commit c663d0c8150ca47a29fe2288709d43d296efe251
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Dec 27 10:02:48 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Dec 27 10:02:48 2019 +0100

    x86/mm: drop redundant smp_wmb() from _put_final_page_type()
    
    get_page_light()'s use of cmpxchg() is a full barrier already anyway.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index b48777cc19..cc0d71996c 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2571,6 +2571,8 @@ int get_page(struct page_info *page, struct domain 
*domain)
  * - it will not be called more than once without dropping the thus
  *   acquired reference again.
  * Due to get_page() reserving one reference, this call cannot fail.
+ *
+ * Note that some callers rely on this being a full memory barrier.
  */
 static void get_page_light(struct page_info *page)
 {
@@ -2755,7 +2757,7 @@ static int _put_final_page_type(struct page_info *page, 
unsigned long type,
     else
     {
         BUG_ON(rc != -ERESTART);
-        smp_wmb();
+        /* get_page_light() includes a full barrier. */
         get_page_light(page);
         page->u.inuse.type_info |= PGT_partial;
     }
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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