linux-kernel - Re: [syzbot] [net?] INFO: rcu detected stall in fq_pie

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Date: Fri, 29 Dec 2023 18:45:51 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+15c3ba3f7ca8ced0914d@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] INFO: rcu detected stall in fq_pie_timer (2)

On Wed, 27 Dec 2023 05:54:18 -0800
> HEAD commit:    7c5e046bdcb2 Merge tag 'net-6.7-rc7' of git://git.kernel.o..
> git tree:       net
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1127e71ae80000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  master

--- x/net/sched/sch_fq_pie.c
+++ y/net/sched/sch_fq_pie.c
@@ -385,8 +385,7 @@ static void fq_pie_timer(struct timer_li
 	root_lock = qdisc_lock(qdisc_root_sleeping(sch));
 	spin_lock(root_lock);
 
-	/* Limit this expensive loop to 2048 flows per round. */
-	max_cnt = min_t(int, q->flows_cnt - q->flows_cursor, 2048);
+	max_cnt = min_t(int, q->flows_cnt - q->flows_cursor, 512);
 	for (i = 0; i < max_cnt; i++) {
 		pie_calculate_probability(&q->p_params,
 					  &q->flows[q->flows_cursor].vars,
@@ -401,7 +400,7 @@ static void fq_pie_timer(struct timer_li
 		next = tupdate;
 	}
 	if (tupdate)
-		mod_timer(&q->adapt_timer, jiffies + next);
+		mod_timer(&q->adapt_timer, jiffies + max(2, next));
 	spin_unlock(root_lock);
 	rcu_read_unlock();
 }
--