[PATCH v3 3/3] mm/armv6: work around armv6 cmpxchg support issue

[Alex Shi]

seems there are couples archs can not do cmpxchg1
So update the patch here. And it's easy to fix if more arch issue find here.

>From cdf98ae7b5e83bb7210c927d4749f62fee4ed115 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi at linux.alibaba.com>
Date: Mon, 31 Aug 2020 15:41:20 +0800
Subject: [PATCH v4 3/3] mm/pageblock: work around multiple arch's cmpxchg
 support issue

Armv6, sh2, sparc32 and xtensa can not do cmpxchg1, so we have to use
cmpxchg4 on it.

arm-linux-gnueabi-ld: mm/page_alloc.o: in function `set_pfnblock_flags_mask':
(.text+0x32b4): undefined reference to `__bad_cmpxchg'
arm-linux-gnueabi-ld: (.text+0x32e0): undefined reference to `__bad_cmpxchg'

Reported-by: kernel test robot <lkp at intel.com>
Signed-off-by: Alex Shi <alex.shi at linux.alibaba.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Baolin Wang <baolin.wang at linux.alibaba.com>
Cc: Russell King <linux at armlinux.org.uk>
Cc: linux-mm at kvack.org
Cc: linux-kernel at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
---
 include/linux/mmzone.h | 20 +++++++++++++++++---
 mm/page_alloc.c        | 24 ++++++++++++------------
 2 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index be676e659fb7..364b29ed99b3 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -406,6 +406,20 @@ enum zone_type {
 
 #ifndef __GENERATING_BOUNDS_H
 
+/*
+ * cmpxchg only support 32-bits operands on the following archs ARMv6, SPARC32
+ * sh2, XTENSA.
+ */
+#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_SH2) || \
+	defined(CONFIG_SPARC32) || defined(CONFIG_XTENSA)
+
+#define BITS_PER_FLAGS	BITS_PER_LONG
+typedef unsigned long pageblockflags_t;
+#else
+#define BITS_PER_FLAGS	BITS_PER_BYTE
+typedef unsigned char pageblockflags_t;
+#endif
+
 struct zone {
 	/* Read-mostly fields */
 
@@ -437,7 +451,7 @@ struct zone {
 	 * Flags for a pageblock_nr_pages block. See pageblock-flags.h.
 	 * In SPARSEMEM, this map is stored in struct mem_section
 	 */
-	unsigned char		*pageblock_flags;
+	pageblockflags_t	*pageblock_flags;
 #endif /* CONFIG_SPARSEMEM */
 
 	/* zone_start_pfn == zone_start_paddr >> PAGE_SHIFT */
@@ -1159,7 +1173,7 @@ struct mem_section_usage {
 	DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
 #endif
 	/* See declaration of similar field in struct zone */
-	unsigned char	pageblock_flags[0];
+	pageblockflags_t	pageblock_flags[0];
 };
 
 void subsection_map_init(unsigned long pfn, unsigned long nr_pages);
@@ -1212,7 +1226,7 @@ struct mem_section {
 extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
 #endif
 
-static inline unsigned char *section_to_usemap(struct mem_section *ms)
+static inline pageblockflags_t *section_to_usemap(struct mem_section *ms)
 {
 	return ms->usage->pageblock_flags;
 }
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 60342e764090..9a41c5dc78eb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -445,7 +445,7 @@ static inline bool defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
 #endif
 
 /* Return a pointer to the bitmap storing bits affecting a block of pages */
-static inline unsigned char *get_pageblock_bitmap(struct page *page,
+static inline pageblockflags_t *get_pageblock_bitmap(struct page *page,
 							unsigned long pfn)
 {
 #ifdef CONFIG_SPARSEMEM
@@ -474,24 +474,24 @@ static inline int pfn_to_bitidx(struct page *page, unsigned long pfn)
  * Return: pageblock_bits flags
  */
 static __always_inline
-unsigned char __get_pfnblock_flags_mask(struct page *page,
+pageblockflags_t __get_pfnblock_flags_mask(struct page *page,
 					unsigned long pfn,
 					unsigned long mask)
 {
-	unsigned char *bitmap;
+	pageblockflags_t *bitmap;
 	unsigned long bitidx, byte_bitidx;
-	unsigned char byte;
+	pageblockflags_t byte;
 
 	bitmap = get_pageblock_bitmap(page, pfn);
 	bitidx = pfn_to_bitidx(page, pfn);
-	byte_bitidx = bitidx / BITS_PER_BYTE;
-	bitidx &= (BITS_PER_BYTE-1);
+	byte_bitidx = bitidx / BITS_PER_FLAGS;
+	bitidx &= (BITS_PER_FLAGS - 1);
 
 	byte = bitmap[byte_bitidx];
 	return (byte >> bitidx) & mask;
 }
 
-unsigned char get_pfnblock_flags_mask(struct page *page, unsigned long pfn,
+pageblockflags_t get_pfnblock_flags_mask(struct page *page, unsigned long pfn,
 					unsigned long mask)
 {
 	return __get_pfnblock_flags_mask(page, pfn, mask);
@@ -513,17 +513,17 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
 					unsigned long pfn,
 					unsigned long mask)
 {
-	unsigned char *bitmap;
+	pageblockflags_t *bitmap;
 	unsigned long bitidx, byte_bitidx;
-	unsigned char old_byte, byte;
+	pageblockflags_t old_byte, byte;
 
-	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != BITS_PER_BYTE);
+	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != BITS_PER_FLAGS);
 	BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));
 
 	bitmap = get_pageblock_bitmap(page, pfn);
 	bitidx = pfn_to_bitidx(page, pfn);
-	byte_bitidx = bitidx / BITS_PER_BYTE;
-	bitidx &= (BITS_PER_BYTE-1);
+	byte_bitidx = bitidx / BITS_PER_FLAGS;
+	bitidx &= (BITS_PER_FLAGS - 1);
 
 	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
 
-- 
1.8.3.1