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Message-Id: <20241213110305.1839-1-hdanton@sina.com>
Date: Fri, 13 Dec 2024 19:03:05 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+00a022dc9979d67df050@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernel?] WARNING in enqueue_dl_entity
On Fri, 22 Nov 2024 14:48:23 -0800
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 28eb75e178d3 Merge tag 'drm-next-2024-11-21' of https://gi..
> git tree: upstream
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1016fec0580000
Test fix (https://lore.kernel.org/lkml/20241213032244.877029-1-vineeth@bitbyteword.org/ )
#syz test upstream master
diff -pur x/include/linux/sched.h y/include/linux/sched.h
--- x/include/linux/sched.h 2024-12-13 18:53:21.592682100 +0800
+++ y/include/linux/sched.h 2024-12-13 18:55:17.754180400 +0800
@@ -656,6 +656,12 @@ struct sched_dl_entity {
* @dl_defer_armed tells if the deferrable server is waiting
* for the replenishment timer to activate it.
*
+ * @dl_server_active tells if the dlserver is active(started).
+ * dlserver is started on first cfs enqueue on an idle runqueue
+ * and is stopped when a dequeue results in 0 cfs tasks on the
+ * runqueue. In other words, dlserver is active only when cpu's
+ * runqueue has atleast one cfs task.
+ *
* @dl_defer_running tells if the deferrable server is actually
* running, skipping the defer phase.
*/
@@ -664,6 +670,7 @@ struct sched_dl_entity {
unsigned int dl_non_contending : 1;
unsigned int dl_overrun : 1;
unsigned int dl_server : 1;
+ unsigned int dl_server_active : 1;
unsigned int dl_defer : 1;
unsigned int dl_defer_armed : 1;
unsigned int dl_defer_running : 1;
diff -pur x/kernel/sched/deadline.c y/kernel/sched/deadline.c
--- x/kernel/sched/deadline.c 2024-12-13 18:51:17.093081100 +0800
+++ y/kernel/sched/deadline.c 2024-12-13 18:55:17.770211500 +0800
@@ -1647,6 +1647,7 @@ void dl_server_start(struct sched_dl_ent
if (!dl_se->dl_runtime)
return;
+ dl_se->dl_server_active = 1;
enqueue_dl_entity(dl_se, ENQUEUE_WAKEUP);
if (!dl_task(dl_se->rq->curr) || dl_entity_preempt(dl_se, &rq->curr->dl))
resched_curr(dl_se->rq);
@@ -1661,6 +1662,7 @@ void dl_server_stop(struct sched_dl_enti
hrtimer_try_to_cancel(&dl_se->dl_timer);
dl_se->dl_defer_armed = 0;
dl_se->dl_throttled = 0;
+ dl_se->dl_server_active = 0;
}
void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
@@ -2421,8 +2423,10 @@ again:
if (dl_server(dl_se)) {
p = dl_se->server_pick_task(dl_se);
if (!p) {
- dl_se->dl_yielded = 1;
- update_curr_dl_se(rq, dl_se, 0);
+ if (dl_server_active(dl_se)) {
+ dl_se->dl_yielded = 1;
+ update_curr_dl_se(rq, dl_se, 0);
+ }
goto again;
}
rq->dl_server = dl_se;
diff -pur x/kernel/sched/fair.c y/kernel/sched/fair.c
--- x/kernel/sched/fair.c 2024-12-13 18:50:13.649803300 +0800
+++ y/kernel/sched/fair.c 2024-12-13 18:56:11.779225700 +0800
@@ -1159,8 +1159,6 @@ static inline void update_curr_task(stru
trace_sched_stat_runtime(p, delta_exec);
account_group_exec_runtime(p, delta_exec);
cgroup_account_cputime(p, delta_exec);
- if (p->dl_server)
- dl_server_update(p->dl_server, delta_exec);
}
static inline bool did_preempt_short(struct cfs_rq *cfs_rq, struct sched_entity *curr)
@@ -1237,11 +1235,16 @@ static void update_curr(struct cfs_rq *c
update_curr_task(p, delta_exec);
/*
- * Any fair task that runs outside of fair_server should
- * account against fair_server such that it can account for
- * this time and possibly avoid running this period.
+ * If the fair_server is active, we need to account for the
+ * fair_server time whether or not the task is running on
+ * behalf of fair_server or not:
+ * - If the task is running on behalf of fair_server, we need
+ * to limit its time based on the assigned runtime.
+ * - Fair task that runs outside of fair_server should account
+ * against fair_server such that it can account for this time
+ * and possibly avoid running this period.
*/
- if (p->dl_server != &rq->fair_server)
+ if (dl_server_active(&rq->fair_server))
dl_server_update(&rq->fair_server, delta_exec);
}
diff -pur x/kernel/sched/sched.h y/kernel/sched/sched.h
--- x/kernel/sched/sched.h 2024-12-13 18:50:42.985005300 +0800
+++ y/kernel/sched/sched.h 2024-12-13 18:55:17.801793100 +0800
@@ -398,6 +398,11 @@ extern void __dl_server_attach_root(stru
extern int dl_server_apply_params(struct sched_dl_entity *dl_se,
u64 runtime, u64 period, bool init);
+static inline bool dl_server_active(struct sched_dl_entity *dl_se)
+{
+ return dl_se->dl_server_active;
+}
+
#ifdef CONFIG_CGROUP_SCHED
extern struct list_head task_groups;
--
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