[PATCH v4 3/4] mm/pageblock: work around multiple arch's cmpxchg support issue

Alex Shi
2020-09-03T07:01:50Z

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

Here we mark above 4 arch's NO_CMPXCHG_BYTE, and would add more if we
found.

This is the first usages of cmpxchg flase sharing change. We'd better
check more cmpxchg usages in current kernel...

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-sh@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: linux-mm@kvack.org
---
arch/Kconfig | 3 +++
arch/arm/Kconfig | 1 +
arch/sh/Kconfig | 1 +
arch/sparc/Kconfig | 1 +
arch/xtensa/Kconfig | 1 +
include/linux/mmzone.h | 15 ++++++++++++---
mm/page_alloc.c | 22 +++++++++++-----------
7 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index af14a567b493..3514570c0f5f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -431,6 +431,9 @@ config HAVE_CMPXCHG_LOCAL
config HAVE_CMPXCHG_DOUBLE
bool

+config NO_CMPXCHG_BYTE
+ bool
+
config ARCH_WEAK_RELEASE_ACQUIRE
bool

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index e00d94b16658..03a6c7fd999d 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -48,6 +48,7 @@ config ARM
select GENERIC_ALLOCATOR
select GENERIC_ARCH_TOPOLOGY if ARM_CPU_TOPOLOGY
select GENERIC_ATOMIC64 if CPU_V7M || CPU_V6 || !CPU_32v6K || !AEABI
+ select NO_CMPXCHG_BYTE if CPU_V6
select GENERIC_CLOCKEVENTS_BROADCAST if SMP
select GENERIC_CPU_AUTOPROBE
select GENERIC_EARLY_IOREMAP
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index d20927128fce..4c7f0ad5b93f 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -155,6 +155,7 @@ menu "System type"
config CPU_SH2
bool
select SH_INTC
+ select NO_CMPXCHG_BYTE

config CPU_SH2A
bool
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index efeff2c896a5..51ae5c8ede87 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -58,6 +58,7 @@ config SPARC32
select CLZ_TAB
select HAVE_UID16
select OLD_SIGACTION
+ select NO_CMPXCHG_BYTE

config SPARC64
def_bool 64BIT
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index e997e0119c02..862b008ab09e 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -42,6 +42,7 @@ config XTENSA
select MODULES_USE_ELF_RELA
select PERF_USE_VMALLOC
select VIRT_TO_BUS
+ select NO_CMPXCHG_BYTE
help
Xtensa processors are 32-bit RISC machines designed by Tensilica
primarily for embedded systems. These processors are both
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index be676e659fb7..0bc5ac0f8cd7 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -406,6 +406,15 @@ enum zone_type {

#ifndef __GENERATING_BOUNDS_H

+/* cmpxchg only support 32-bits operands on ARMv6, SPARC32, sh2, XTENSA.*/
+#ifdef CONFIG_NO_CMPXCHG_BYTE
+#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 +446,7 @@ 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 +1168,7 @@ 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 +1221,7 @@ 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 3688e6b83318..8b65d83d8be6 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);
@@ -513,16 +513,16 @@ 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;
+ byte_bitidx = bitidx / BITS_PER_FLAGS;

VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);

--
1.8.3.1