[PATCH] mm/vmstat: reject invalid stat_interval values

Cao Ruichuang
2026-04-10T11:26:27Z

vm.stat_interval is exposed in seconds, but proc_dointvec_jiffies()
currently accepts zero and negative values. In the current tree,
writing 0 succeeds and leaves /proc/sys/vm/stat_interval at 0.

vmstat_update() uses the stored jiffy interval directly when it
requeues its delayed work, so a zero interval can drive excessive
kworker CPU usage. Negative values are not meaningful either.

Switch vm.stat_interval to a small custom sysctl handler that keeps
the existing seconds-based userspace ABI while rejecting values below
1 and capping the upper bound at INT_MAX / HZ.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=220226
Signed-off-by: Cao Ruichuang <create0818@163.com>
---
mm/vmstat.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 86b14b0f77b..f48d3bdad64 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1964,6 +1964,7 @@ static const struct seq_operations vmstat_op = {
#ifdef CONFIG_SMP
static DEFINE_PER_CPU(struct delayed_work, vmstat_work);
static int sysctl_stat_interval __read_mostly = HZ;
+static const int sysctl_stat_interval_max = INT_MAX / HZ;
static int vmstat_late_init_done;

#ifdef CONFIG_PROC_FS
@@ -1972,6 +1973,26 @@ static void refresh_vm_stats(struct work_struct *work)
refresh_cpu_vm_stats(true);
}

+static int vmstat_stat_interval_handler(const struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ int interval = sysctl_stat_interval / HZ;
+ const struct ctl_table tmp = {
+ .data = &interval,
+ .maxlen = sizeof(interval),
+ .mode = table->mode,
+ .extra1 = SYSCTL_ONE,
+ .extra2 = (void *)&sysctl_stat_interval_max,
+ };
+ int ret;
+
+ ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+ if (!ret && write)
+ sysctl_stat_interval = interval * HZ;
+
+ return ret;
+}
+
static int vmstat_refresh(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
@@ -2236,7 +2257,7 @@ static const struct ctl_table vmstat_table[] = {
.data = &sysctl_stat_interval,
.maxlen = sizeof(sysctl_stat_interval),
.mode = 0644,
- .proc_handler = proc_dointvec_jiffies,
+ .proc_handler = vmstat_stat_interval_handler,
},
{
.procname = "stat_refresh",
--
2.39.5 (Apple Git-154)