[PATCH 1/4] mm: restore node stat checking in /proc/sys/vm/stat_refresh

[Hugh Dickins]

v4.7 52b6f46bc163 ("mm: /proc/sys/vm/stat_refresh to force vmstat update")
introduced vmstat_refresh(), with its vmstat underflow checking; then
v4.8 75ef71840539 ("mm, vmstat: add infrastructure for per-node vmstats")
split NR_VM_NODE_STAT_ITEMS out of NR_VM_ZONE_STAT_ITEMS without updating
vmstat_refresh(): so it has been missing out much of the vmstat underflow
checking ever since. Reinstate it. Thanks to Roman Gushchin <guro@xxxxxx>
for tangentially pointing this out.

Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---

 mm/vmstat.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- 5.12-rc/mm/vmstat.c	2021-02-24 12:03:55.000000000 -0800
+++ vmstat1/mm/vmstat.c	2021-02-25 11:50:36.000000000 -0800
@@ -1857,6 +1857,14 @@ int vmstat_refresh(struct ctl_table *tab
 		}
 	}
 #endif
+	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) {
+		val = atomic_long_read(&vm_node_stat[i]);
+		if (val < 0) {
+			pr_warn("%s: %s %ld\n",
+				__func__, node_stat_name(i), val);
+			err = -EINVAL;
+		}
+	}
 	if (err)
 		return err;
 	if (write)