Re: [akpm-mm:mm-unstable 313/322] include/linux/huge_mm.h:274:23: error: variably modified 'stats' at file scope

[Barry Song <21cnbao@gmail.com>]

> 
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> head:   f43b3aae94511d62174c3b29239da0dd22d0eeb3
> commit: d4358ee0a075e232114dfec0cd162860cfa2771b [313/322] mm: add per-order mTHP anon_alloc and anon_alloc_fallback counters
> config: powerpc-allmodconfig (https://download.01.org/0day-ci/archive/20240406/202404061627.ungVloow-lkp@intel.com/config)
> compiler: powerpc64-linux-gcc (GCC) 13.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240406/202404061627.ungVloow-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202404061627.ungVloow-lkp@intel.com/

> All errors (new ones prefixed by >>):
> 
>    In file included from include/linux/mm.h:1115,
>                     from include/linux/mman.h:5,
>                     from arch/powerpc/kernel/asm-offsets.c:19:
>>> include/linux/huge_mm.h:274:23: error: variably modified 'stats' at file scope
>      274 |         unsigned long stats[PMD_ORDER + 1][__MTHP_STAT_COUNT];
>          |                       ^~~~~
>    make[3]: *** [scripts/Makefile.build:117: arch/powerpc/kernel/asm-offsets.s] Error 1

Should have been fixed by:

From 573aa50dbebcd4b2650d477374b28aa53c21b968 Mon Sep 17 00:00:00 2001
From: Barry Song <v-songbaohua@oppo.com>
Date: Sun, 7 Apr 2024 12:23:35 +1200
Subject: [PATCH] mm: fix powerpc build issue

Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 include/linux/huge_mm.h |  9 ++++-----
 mm/huge_memory.c        | 13 +++++++++++--
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index c5d33017a4dd..0717063dc5e7 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -271,16 +271,15 @@ enum mthp_stat_item {
 };
 
 struct mthp_stat {
-	unsigned long stats[PMD_ORDER + 1][__MTHP_STAT_COUNT];
+	unsigned long stats[0][__MTHP_STAT_COUNT];
 };
 
-DECLARE_PER_CPU(struct mthp_stat, mthp_stats);
+extern struct mthp_stat __percpu *mthp_stats;
 
 static inline void count_mthp_stat(int order, enum mthp_stat_item item)
 {
-	if (unlikely(order > PMD_ORDER))
-		return;
-	this_cpu_inc(mthp_stats.stats[order][item]);
+	if (likely(order <= PMD_ORDER))
+		raw_cpu_ptr(mthp_stats)->stats[order][item]++;
 }
 
 #define transparent_hugepage_use_zero_page()				\
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5b875f0fc923..10bc3f54cb81 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -526,7 +526,7 @@ static const struct kobj_type thpsize_ktype = {
 	.sysfs_ops = &kobj_sysfs_ops,
 };
 
-DEFINE_PER_CPU(struct mthp_stat, mthp_stats) = {{{0}}};
+struct mthp_stat __percpu *mthp_stats;
 
 static unsigned long sum_mthp_stat(int order, enum mthp_stat_item item)
 {
@@ -534,7 +534,7 @@ static unsigned long sum_mthp_stat(int order, enum mthp_stat_item item)
 	int cpu;
 
 	for_each_online_cpu(cpu) {
-		struct mthp_stat *this = &per_cpu(mthp_stats, cpu);
+		struct mthp_stat *this = per_cpu_ptr(mthp_stats, cpu);
 
 		sum += this->stats[order][item];
 	}
@@ -602,6 +602,7 @@ static struct thpsize *thpsize_create(int order, struct kobject *parent)
 static void thpsize_release(struct kobject *kobj)
 {
 	kfree(to_thpsize(kobj));
+	free_percpu(mthp_stats);
 }
 
 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
@@ -636,6 +637,13 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 		goto remove_hp_group;
 	}
 
+	mthp_stats = (struct mthp_stat __percpu *)alloc_percpu((PMD_ORDER + 1) *
+					sizeof(sizeof(mthp_stats->stats[0])));
+	if (!mthp_stats) {
+		err = -ENOMEM;
+		goto remove_hp_group;
+	}
+
 	orders = THP_ORDERS_ALL_ANON;
 	order = highest_order(orders);
 	while (orders) {
@@ -673,6 +681,7 @@ static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 	sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 	sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 	kobject_put(hugepage_kobj);
+	free_percpu(mthp_stats);
 }
 #else
 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
-- 
2.34.1