[PATCH v2 2/4] sched/deadline: fix inactive_task_timer splat

Wander Lairson Costa
2023-01-20T15:04:31Z

inactive_task_timer() executes in interrupt (atomic) context. It calls
put_task_struct(), which indirectly acquires sleeping locks under
PREEMPT_RT.

Below is an example of a splat that happened in a test environment:

CPU: 1 PID: 2848 Comm: life Kdump: loaded Tainted: G W ---------
Hardware name: HP ProLiant DL388p Gen8, BIOS P70 07/15/2012
Call Trace:
dump_stack_lvl+0x57/0x7d
mark_lock_irq.cold+0x33/0xba
? stack_trace_save+0x4b/0x70
? save_trace+0x55/0x150
mark_lock+0x1e7/0x400
mark_usage+0x11d/0x140
__lock_acquire+0x30d/0x930
lock_acquire.part.0+0x9c/0x210
? refill_obj_stock+0x3d/0x3a0
? rcu_read_lock_sched_held+0x3f/0x70
? trace_lock_acquire+0x38/0x140
? lock_acquire+0x30/0x80
? refill_obj_stock+0x3d/0x3a0
rt_spin_lock+0x27/0xe0
? refill_obj_stock+0x3d/0x3a0
refill_obj_stock+0x3d/0x3a0
? inactive_task_timer+0x1ad/0x340
kmem_cache_free+0x357/0x560
inactive_task_timer+0x1ad/0x340
? switched_from_dl+0x2d0/0x2d0
__run_hrtimer+0x8a/0x1a0
__hrtimer_run_queues+0x91/0x130
hrtimer_interrupt+0x10f/0x220
__sysvec_apic_timer_interrupt+0x7b/0xd0
sysvec_apic_timer_interrupt+0x4f/0xd0
? asm_sysvec_apic_timer_interrupt+0xa/0x20
asm_sysvec_apic_timer_interrupt+0x12/0x20
RIP: 0033:0x7fff196bf6f5

Use put_task_struct_atomic_safe() instead.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
kernel/sched/deadline.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0d97d54276cc..03400c61a994 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1442,7 +1442,7 @@ static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer)
dl_se->dl_non_contending = 0;
unlock:
task_rq_unlock(rq, p, &rf);
- put_task_struct(p);
+ put_task_struct_atomic_safe(p);

return HRTIMER_NORESTART;
}
--
2.39.0