[PATCH] mm/vmstat: fix outdated vmstat_text

[Jann Horn <jannh@google.com>]

commit 7a9cdebdcc17 ("mm: get rid of vmacache_flush_all() entirely")
removed the VMACACHE_FULL_FLUSHES statistics, but didn't remove the
corresponding entry in vmstat_text. This causes an out-of-bounds access in
vmstat_show().

Luckily this only affects kernels with CONFIG_DEBUG_VM_VMACACHE=y, which is
probably very rare.

Having two gigantic arrays that must be kept in sync isn't exactly robust.
To make it easier to catch such issues in the future, add a BUILD_BUG_ON().

Fixes: 7a9cdebdcc17 ("mm: get rid of vmacache_flush_all() entirely")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
---
 mm/vmstat.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 8ba0870ecddd..db6379a3f8bf 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1283,7 +1283,6 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_DEBUG_VM_VMACACHE
 	"vmacache_find_calls",
 	"vmacache_find_hits",
-	"vmacache_full_flushes",
 #endif
 #ifdef CONFIG_SWAP
 	"swap_ra",
@@ -1661,6 +1660,8 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 	stat_items_size += sizeof(struct vm_event_state);
 #endif
 
+	BUILD_BUG_ON(stat_items_size !=
+		     ARRAY_SIZE(vmstat_text) * sizeof(unsigned long));
 	v = kmalloc(stat_items_size, GFP_KERNEL);
 	m->private = v;
 	if (!v)
-- 
2.19.0.605.g01d371f741-goog