On Tue, May 11, 2021 at 08:31:23AM -0400, Andrea Arcangeli wrote:
> Hello,
> 
> thanks to the report.
> 
> Peter, this isn't immediately clear to me, is it perhaps something
> related to clang?
> 
> This is commit 8dec302e87453234fc7ac1cf4d09e4d577a06cf3

Andrea,

I guess it's probably a NOMMU arm config so the helper got opted out as I
errornously put it into a CONFIG_MMU block without noticing..

So we may need to squash below into that commit.

I really should think of something to avoid such errors in the future, as this
is the 2nd time happening at least this year..  Probably I should always start
adding helpers at the beginning of files so I won't overlook any macros..

Thanks,

----8<----
diff --git a/mm/gup.c b/mm/gup.c
index bb130723a6717..0223644d0c61a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -392,6 +392,17 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
 }
 EXPORT_SYMBOL(unpin_user_pages);
 
+/*
+ * Set the MMF_HAS_PINNED if not set yet; after set it'll be there for the mm's
+ * lifecycle.  Avoid setting the bit unless necessary, or it might cause write
+ * cache bouncing on large SMP machines for concurrent pinned gups.
+ */
+static inline void mm_set_has_pinned_flag(unsigned long *mm_flags)
+{
+       if (!test_bit(MMF_HAS_PINNED, mm_flags))
+               set_bit(MMF_HAS_PINNED, mm_flags);
+}
+
 #ifdef CONFIG_MMU
 static struct page *no_page_table(struct vm_area_struct *vma,
                unsigned int flags)
@@ -1270,17 +1281,6 @@ int fixup_user_fault(struct mm_struct *mm,
 }
 EXPORT_SYMBOL_GPL(fixup_user_fault);
 
-/*
- * Set the MMF_HAS_PINNED if not set yet; after set it'll be there for the mm's
- * lifecycle.  Avoid setting the bit unless necessary, or it might cause write
- * cache bouncing on large SMP machines for concurrent pinned gups.
- */
-static inline void mm_set_has_pinned_flag(unsigned long *mm_flags)
-{
-       if (!test_bit(MMF_HAS_PINNED, mm_flags))
-               set_bit(MMF_HAS_PINNED, mm_flags);
-}
-
 /*
  * Please note that this function, unlike __get_user_pages will not
  * return 0 for nr_pages > 0 without FOLL_NOWAIT
----8<----

-- 
Peter Xu