[PATCH v2 2/3] sched/fair: Fix panic if pick_eevdf() returns NULL

From: Adam Li
Date: Wed Nov 27 2024 - 00:57:16 EST


pick_eevdf() may return NULL, which triggers NULL pointer
dereference at pick_next_entity():
struct sched_entity *se = pick_eevdf(cfs_rq);
if (se->sched_delayed)

[ 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

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

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cd1188b7f3df..d5a3b5589e4e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5623,7 +5623,7 @@ pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
}

struct sched_entity *se = pick_eevdf(cfs_rq);
- if (se->sched_delayed) {
+ if (se && se->sched_delayed) {
dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
/*
* Must not reference @se again, see __block_task().
--
2.25.1