include/linux/swapops.h: correct guards for non_swap_entry()

If CONFIG_DEVICE_PRIVATE is defined, but neither CONFIG_MEMORY_FAILURE nor
CONFIG_MIGRATION, then non_swap_entry() will return 0, meaning that the
condition (non_swap_entry(entry) && is_device_private_entry(entry)) in
zap_pte_range() will never be true even if the entry is a device private
one.

Equally any other code depending on non_swap_entry() will not function as
expected.

I originally spotted this just by looking at the code, I haven't actually
observed any problems.

Looking a bit more closely it appears that actually this situation
(currently at least) cannot occur:

DEVICE_PRIVATE depends on ZONE_DEVICE
ZONE_DEVICE depends on MEMORY_HOTREMOVE
MEMORY_HOTREMOVE depends on MIGRATION

Fixes: 5042db43cc26 ("mm/ZONE_DEVICE: new type of ZONE_DEVICE for unaddressable memory")
Signed-off-by: Steven Price <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Jérôme Glisse <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: John Hubbard <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 9a6f06de183b..d9b7c9132c2f 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -350,7 +350,8 @@ static inline void num_poisoned_pages_inc(void)
 }
 #endif
 
-#if defined(CONFIG_MEMORY_FAILURE) || defined(CONFIG_MIGRATION)
+#if defined(CONFIG_MEMORY_FAILURE) || defined(CONFIG_MIGRATION) || \
+    defined(CONFIG_DEVICE_PRIVATE)
 static inline int non_swap_entry(swp_entry_t entry)
 {
 	return swp_type(entry) >= MAX_SWAPFILES;