[PATCH nf v3 1/1] ipvs: stop estimator after disabled calc phase

IPVS estimator kthread 0 starts with zeroed chain and tick limits until
its initial calculation phase completes. If network namespace teardown
clears ipvs->enable during that phase, ip_vs_est_calc_phase() can return
without installing positive limits.

The kthread can then continue into its main loop and drain
est_temp_list with zero chain_max, tick_max and est_max_count values.
Each enqueue consumes one available tick row, but est_count never
reaches the zero est_max_count value. After all rows are consumed, the
row lookup returns IPVS_EST_NTICKS and ip_vs_enqueue_estimator() writes
past the ticks and tick_len arrays.

Exit kthread 0 after the calculation phase if the kthread is stopping or
IPVS has been disabled. That keeps temporary estimators from being
drained after the limits failed to initialize.

Estimator kthreads can now self-exit before teardown or reload stops
kd->task. Keep an extra task reference after creation and release it
with kthread_stop_put(), so kd->task remains valid until the stop paths
consume that reference.

Fixes: 705dd3444081 ("ipvs: use kthreads for stats estimation")
Cc: [email protected]
Reported-by: Vega <[email protected]>
Signed-off-by: Zhiling Zou <[email protected]>
---
changes in v3:
- Keep an extra task_struct reference for estimator kthreads and
  release it with kthread_stop_put(), as suggested by Julian
  Anastasov, so self-exiting kthreads do not leave kd->task dangling.
- v2 Link: https://lore.kernel.org/all/03a7ee4873f9dfc51add97df5b67bf0b0d793dbe.1785211268.git.zhilinz@nebusec.ai

changes in v2:
- Exit the estimator kthread after the calculation phase if IPVS
  has been disabled or the kthread is stopping, as suggested by
  Julian Anastasov.
- Drop the later enqueue and drain guards from v1.
- v1 Link: https://lore.kernel.org/all/6359e0031f0ee7cc969bae3483308de362d3c709.1784878022.git.zhilinz@nebusec.ai

 net/netfilter/ipvs/ip_vs_est.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_est.c b/net/netfilter/ipvs/ip_vs_est.c
index ab09f51829512..05a216a47b45e 100644
--- a/net/netfilter/ipvs/ip_vs_est.c
+++ b/net/netfilter/ipvs/ip_vs_est.c
@@ -191,8 +191,11 @@ static int ip_vs_estimation_kthread(void *data)
 		}
 
 		/* kthread 0 will handle the calc phase */
-		if (ipvs->est_calc_phase)
+		if (ipvs->est_calc_phase) {
 			ip_vs_est_calc_phase(ipvs);
+			if (kthread_should_stop() || !READ_ONCE(ipvs->enable))
+				return 0;
+		}
 	}
 
 	while (1) {
@@ -270,6 +273,7 @@ int ip_vs_est_kthread_start(struct netns_ipvs *ipvs,
 		kd->task = NULL;
 		goto out;
 	}
+	get_task_struct(kd->task);
 
 	set_user_nice(kd->task, sysctl_est_nice(ipvs));
 	if (sysctl_est_preferred_cpulist(ipvs))
@@ -286,7 +290,7 @@ void ip_vs_est_kthread_stop(struct ip_vs_est_kt_data *kd)
 {
 	if (kd->task) {
 		pr_info("stopping estimator thread %d...\n", kd->id);
-		kthread_stop(kd->task);
+		kthread_stop_put(kd->task);
 		kd->task = NULL;
 	}
 }
@@ -526,7 +530,7 @@ static void ip_vs_est_kthread_destroy(struct ip_vs_est_kt_data *kd)
 	if (kd) {
 		if (kd->task) {
 			pr_info("stop unused estimator thread %d...\n", kd->id);
-			kthread_stop(kd->task);
+			kthread_stop_put(kd->task);
 		}
 		ip_vs_stats_free(kd->calc_stats);
 		kfree(kd);
-- 
2.43.0