[PATCH] mm: Fix clang W=1 compiler warnings

[Bart Van Assche <bvanassche@acm.org>]

Commit 30c2de0a267c ("mm/vmstat: fix a W=1 clang compiler warning")
suppresses some but not all compiler warnings that are reported by clang
when building mm/ with W=1. Hence revert commit 30c2de0a267c and instead
make NR_LRU_BASE and NR_ZONE_LRU_BASE integer constants instead of
enumeration constants. Additionally, convert the item##_NORMAL constants
from type enum vm_event_item into int before subtracting ZONE_NORMAL. The
latter constant has type enum zone_type.

Cc: Ivan Shapovalov <intelfx@intelfx.name>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: David Laight <david.laight@aculab.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 include/linux/mmzone.h | 26 +++++++++++++++++++++-----
 include/linux/vmstat.h |  9 +++++++--
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9540b41894da..bc139c704538 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -135,11 +135,20 @@ enum numa_stat_item {
 #define NR_VM_NUMA_EVENT_ITEMS 0
 #endif
 
+/*
+ * NR_ZONE_LRU_BASE and NR_VM_ZONE_STAT_ITEMS are often added to enumeration
+ * constants of another type than enum_zone_stat_item. Define these constants
+ * as an integer instead of enum node_stat_item to prevent that the compiler
+ * warns about enumeration type mismatches when these constants are used.
+ */
+#define NR_ZONE_LRU_BASE	(__NR_ZONE_LRU_BASE + 0)
+#define NR_VM_ZONE_STAT_ITEMS	(__NR_VM_ZONE_STAT_ITEMS + 0)
+
 enum zone_stat_item {
 	/* First 128 byte cacheline (assuming 64 bit words) */
 	NR_FREE_PAGES,
-	NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
-	NR_ZONE_INACTIVE_ANON = NR_ZONE_LRU_BASE,
+	__NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
+	NR_ZONE_INACTIVE_ANON = __NR_ZONE_LRU_BASE,
 	NR_ZONE_ACTIVE_ANON,
 	NR_ZONE_INACTIVE_FILE,
 	NR_ZONE_ACTIVE_FILE,
@@ -155,11 +164,18 @@ enum zone_stat_item {
 #ifdef CONFIG_UNACCEPTED_MEMORY
 	NR_UNACCEPTED,
 #endif
-	NR_VM_ZONE_STAT_ITEMS };
+	__NR_VM_ZONE_STAT_ITEMS };
+
+/*
+ * enum lru_list constants are often added to NR_LRU_BASE. Define NR_LRU_BASE
+ * as an integer instead of enum node_stat_item to prevent that the compiler
+ * warns about enumeration type mismatches.
+ */
+#define NR_LRU_BASE (__NR_LRU_BASE + 0)
 
 enum node_stat_item {
-	NR_LRU_BASE,
-	NR_INACTIVE_ANON = NR_LRU_BASE, /* must match order of LRU_[IN]ACTIVE */
+	__NR_LRU_BASE,
+	NR_INACTIVE_ANON = __NR_LRU_BASE, /*must match order of LRU_[IN]ACTIVE*/
 	NR_ACTIVE_ANON,		/*  "     "     "   "       "         */
 	NR_INACTIVE_FILE,	/*  "     "     "   "       "         */
 	NR_ACTIVE_FILE,		/*  "     "     "   "       "         */
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 9f3a04345b86..72d1974ee81f 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -135,8 +135,13 @@ static inline void vm_events_fold_cpu(int cpu)
 #define count_vm_vma_lock_event(x) do {} while (0)
 #endif
 
+/*
+ * item##_NORMAL has type enum vm_event_item while ZONE_NORMAL and zid have
+ * type enum zone_type. Suppress compiler warnings about mixing different
+ * enumeration types by converting item##_NORMAL into an int with '+ 0'.
+ */
 #define __count_zid_vm_events(item, zid, delta) \
-	__count_vm_events(item##_NORMAL - ZONE_NORMAL + zid, delta)
+	__count_vm_events((item##_NORMAL + 0) - ZONE_NORMAL + zid, delta)
 
 /*
  * Zone and node-based page accounting with per cpu differentials.
@@ -515,7 +520,7 @@ static inline const char *node_stat_name(enum node_stat_item item)
 
 static inline const char *lru_list_name(enum lru_list lru)
 {
-	return node_stat_name(NR_LRU_BASE + (enum node_stat_item)lru) + 3; // skip "nr_"
+	return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
 }
 
 #if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)