Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH] sched/deadline: fix inactive_task_timer splat with CONFIG_PREEMPT_RT | Date | Thu, 19 Jan 2023 18:03:02 +0000 |
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On 04/01/23 15:17, Wander Lairson Costa wrote: > 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 > > Instead of calling put_task_struct() directly, we defer it using > call_rcu(). A more natural approach would use a workqueue, but since > in PREEMPT_RT, we can't allocate dynamic memory from atomic context, > the code would become more complex because we would need to put the > work_struct instance in the task_struct and initialize it when we > allocate a new task_struct. >
Sorry to come back on this; Juri reminded me offline that put_task_struct() is invoked in other non-sleepable contexts, not just inactive_task_timer().
e.g.
rto_push_irq_work_func() // hard irq work so hardirq context `\ push_rt_task() `\ put_task_struct()
Or
cpu_stopper_thread() // stopper callbacks must not sleep `\ push_cpu_stop() `\ put_task_struct()
... But then again I'm not aware of any splats happening in these paths. Is there something special about inactive_task_timer(), or could it be the issue is there for those other paths but we just haven't had them reported yet?
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