[PATCH] mm/vmstat: reject zero vm.stat_interval to prevent busy-loop

[Maximilian Pezzullo via B4 Relay <devnull+maximilianpezzullo.gmail.com@kernel.org>]

From: Maximilian Pezzullo <maximilianpezzullo@gmail.com>

Setting vm.stat_interval to 0 causes excessive kworker CPU usage
because vmstat_shepherd() and vmstat_update() reschedule themselves
with round_jiffies_relative(0), which resolves to an immediate
reschedule and creates a busy-loop.

Add a custom sysctl handler that rejects 0 and restores the previous
value, similar to how dirtytime_interval_handler() handles
vm.dirtytime_expire_seconds.

Reported-by: Terry M <terrym3201@bugzilla.kernel.org>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220226
Signed-off-by: Maximilian Pezzullo <maximilianpezzullo@gmail.com>
---
 mm/vmstat.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 86b14b0f77b5..6eeb4341b215 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -2114,6 +2114,18 @@ void vmstat_flush_workqueue(void)
 	flush_workqueue(mm_percpu_wq);
 }
 
+static int vmstat_interval_handler(const struct ctl_table *table, int write,
+				    void *buffer, size_t *lenp, loff_t *ppos)
+{
+	int ret = proc_dointvec_jiffies(table, write, buffer, lenp, ppos);
+
+	if (ret == 0 && write && sysctl_stat_interval == 0) {
+		sysctl_stat_interval = HZ;
+		return -EINVAL;
+	}
+	return ret;
+}
+
 static void vmstat_shepherd(struct work_struct *w)
 {
 	int cpu;
@@ -2236,7 +2248,7 @@ 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_interval_handler,
 	},
 	{
 		.procname	= "stat_refresh",

---
base-commit: af4e9ef3d78420feb8fe58cd9a1ab80c501b3c08
change-id: 20260304-mm-vmstat-reject-zero-vm-stat_interval-to-prevent-busy-loop-ba5446a527aa

Best regards,
-- 
Maximilian Pezzullo <maximilianpezzullo@gmail.com>