linux-kernel - [PATCH 1/2] sched/fair: Fix panic if NEXT

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Message-Id: <20241125021222.356881-2-adamli@os.amperecomputing.com>
Date: Mon, 25 Nov 2024 02:12:20 +0000
From: Adam Li <adamli@...amperecomputing.com>
To: peterz@...radead.org,
	mingo@...hat.com,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org
Cc: dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org,
	patches@...erecomputing.com,
	cl@...ux.com,
	Adam Li <adamli@...amperecomputing.com>
Subject: [PATCH 1/2] sched/fair: Fix panic if NEXT_BUDDY enabled

Enabling NEXT_BUDDY may trigger warning and kernel panic:

[  124.977300] cfs_rq->next->sched_delayed
[  124.977310] WARNING: CPU: 51 PID: 2150 at kernel/sched/fair.c:5621 pick_task_fair+0x130/0x150
<snip>
[  297.371198] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000051
[  297.406112] CPU: 116 UID: 0 PID: 10328 Comm: Grizzly-worker( Tainted: G        W   E      6.12.0.adam+ #1
[  297.597362] Call trace:
[  297.599795]  pick_task_fair+0x50/0x150 (P)
[  297.603879]  pick_task_fair+0x50/0x150 (L)
[  297.607963]  pick_next_task_fair+0x30/0x3c0
[  297.612134]  __pick_next_task+0x4c/0x220
[  297.616045]  pick_next_task+0x44/0x980
[  297.619782]  __schedule+0x3d0/0x628
[  297.623259]  do_task_dead+0x50/0x60
[  297.626736]  do_exit+0x28c/0x410
[  297.629955]  do_group_exit+0x3c/0xa0
[  297.633518]  get_signal+0x8c4/0x8d0
[  297.636996]  do_signal+0x9c/0x270
[  297.640299]  do_notify_resume+0xe0/0x198
[  297.644212]  el0_svc+0xf4/0x170
[  297.647342]  el0t_64_sync_handler+0x10c/0x138
[  297.651687]  el0t_64_sync+0x1ac/0x1b0
[  297.655339] Code: d503201f 1400002a aa1403e0 97ffda0b (39414401)
[  297.661439] ---[ end trace 0000000000000000 ]---
[  297.726593] Kernel panic - not syncing: Oops: Fatal exception

Do not set next buddy if sched_delayed is set.

Signed-off-by: Adam Li <adamli@...amperecomputing.com>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fbdca89c677f..cd1188b7f3df 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8748,6 +8748,8 @@ static void set_next_buddy(struct sched_entity *se)
 			return;
 		if (se_is_idle(se))
 			return;
+		if (se->sched_delayed)
+			return;
 		cfs_rq_of(se)->next = se;
 	}
 }
-- 
2.25.1