linux-kernel - [PATCH] mm/vmstat: Fix build with MEMCG=y and VM_EVENT

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Message-ID: <20250604095111.533783-1-kirill.shutemov@linux.intel.com>
Date: Wed,  4 Jun 2025 12:51:11 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>
Cc: lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com,
	vbabka@...e.cz,
	rppt@...nel.org,
	surenb@...gle.com,
	mhocko@...e.com,
	hannes@...xchg.org,
	shakeel.butt@...ux.dev,
	muchun.song@...ux.dev,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Konstantin Khlebnikov <koct9i@...il.com>
Subject: [PATCH] mm/vmstat: Fix build with MEMCG=y and VM_EVENT_COUNTERS=n

When compiling with MEMCG enabled but VM_EVENT_COUNTERS disabled,
BUILD_BUG_ON() is triggered in vmstat_start because the vmstat_text
array is larger than NR_VMSTAT_ITEMS.

This issue arises because some elements of the vmstat_text array are
present when either MEMCG or VM_EVENT_COUNTERS is enabled, but
NR_VMSTAT_ITEMS only accounts for these elements if VM_EVENT_COUNTERS is
enabled.

The recent change in the BUILD_BUG_ON() check made it more strict,
disallowing extra elements in the array, which revealed the issue.

Instead of adjusting the NR_VMSTAT_ITEMS definition to account for
MEMCG, make MEMCG select VM_EVENT_COUNTERS. VM_EVENT_COUNTERS is
enabled in most configurations anyway.

There is no need to backport this fix to stable trees. Without the
strict BUILD_BUG_ON(), the issue is not harmful. The elements in
question would only be read by the memcg code, not by /proc/vmstat.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reported-by: Randy Dunlap <rdunlap@...radead.org>
Fixes: ebc5d83d0443 ("mm/memcontrol: use vmstat names for printing statistics")
Cc: Konstantin Khlebnikov <koct9i@...il.com>
---
 include/linux/vmstat.h | 4 ++--
 init/Kconfig           | 1 +
 mm/vmstat.c            | 4 ++--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index b2ccb6845595..c287998908bf 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -507,7 +507,7 @@ static inline const char *lru_list_name(enum lru_list lru)
 	return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
 }
 
-#if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)
+#if defined(CONFIG_VM_EVENT_COUNTERS)
 static inline const char *vm_event_name(enum vm_event_item item)
 {
 	return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
@@ -516,7 +516,7 @@ static inline const char *vm_event_name(enum vm_event_item item)
 			   NR_VM_STAT_ITEMS +
 			   item];
 }
-#endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
+#endif /* CONFIG_VM_EVENT_COUNTERS */
 
 #ifdef CONFIG_MEMCG
 
diff --git a/init/Kconfig b/init/Kconfig
index ab83abe0fd9d..dd332cac6036 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -989,6 +989,7 @@ config MEMCG
 	select PAGE_COUNTER
 	select EVENTFD
 	select SLAB_OBJ_EXT
+	select VM_EVENT_COUNTERS
 	help
 	  Provides control over the memory footprint of tasks in a cgroup.
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 27dc37168cfd..c3114b8826e4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1301,7 +1301,7 @@ const char * const vmstat_text[] = {
 	[I(NR_MEMMAP_BOOT_PAGES)]		= "nr_memmap_boot_pages",
 #undef I
 
-#if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)
+#if defined(CONFIG_VM_EVENT_COUNTERS)
 	/* enum vm_event_item counters */
 #define I(x) (NR_VM_ZONE_STAT_ITEMS + NR_VM_NUMA_EVENT_ITEMS + \
 	     NR_VM_NODE_STAT_ITEMS + NR_VM_STAT_ITEMS + x)
@@ -1498,7 +1498,7 @@ const char * const vmstat_text[] = {
 #endif
 #endif
 #undef I
-#endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
+#endif /* CONFIG_VM_EVENT_COUNTERS */
 };
 #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */
 
-- 
2.47.2