From: Willy Tarreau <w@1wt.eu>
Date: Wed, 10 Sep 2025 16:45:01 +0000 (+0200)
Subject: BUG/MINOR: stick-table: make sure never to miss a process_table_expire update
X-Git-Tag: v3.3-dev9~151
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2831cb104fa4cb528f27240a33ba84d27d7449b8;p=thirdparty%2Fhaproxy.git

BUG/MINOR: stick-table: make sure never to miss a process_table_expire update

In stktable_requeue_exp(), there's a tiny race at the beginning during
which we check the task's expiration date to decide whether or not to
wake process_table_expire() up. During this race, the task might just
have finished running on its owner thread and we can miss a task_queue()
opportunity, which probably explains why during testing it seldom happens
that a few entries are left at the end.

Let's perform a CAS to confirm the value is still the same before
leaving. This way we're certain that our value has been seen at least
once.

This should be backported to 3.2.
---

diff --git a/src/stick_table.c b/src/stick_table.c
index 54d9699a6..b7f6f89bb 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -724,14 +724,18 @@ void stktable_requeue_exp(struct stktable *t, const struct stksess *ts)
 	old_exp = HA_ATOMIC_LOAD(&t->exp_task->expire);
 	new_exp = tick_first(expire, old_exp);
 
-	/* let's not go further if we're already up to date */
-	if (new_exp == old_exp)
+	/* let's not go further if we're already up to date. We have
+	 * to make sure the compared date doesn't change under us.
+	 */
+	if (new_exp == old_exp &&
+	    HA_ATOMIC_CAS(&t->exp_task->expire, &old_exp, new_exp))
 		return;
 
 	HA_RWLOCK_WRLOCK(STK_TABLE_LOCK, &t->lock);
 
-	while (new_exp != old_exp &&
-	       !HA_ATOMIC_CAS(&t->exp_task->expire, &old_exp, new_exp)) {
+	while (!HA_ATOMIC_CAS(&t->exp_task->expire, &old_exp, new_exp)) {
+		if (new_exp == old_exp)
+			break;
 		__ha_cpu_relax();
 		new_exp = tick_first(expire, old_exp);
 	}