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McKenney" Cc: Steven Rostedt , Anders Roxell , Andrew Morton , Alexander Potapenko , Dmitry Vyukov , Jann Horn , Mark Rutland , Linux Kernel Mailing List , Linux-MM , kasan-dev , rcu@vger.kernel.org, Peter Zijlstra , Tejun Heo , Lai Jiangshan Subject: Re: [PATCH] kfence: Avoid stalling work queue task without allocations Message-ID: <20201119170259.GA2134472@elver.google.com> References: <20201112161439.GA2989297@elver.google.com> <20201112175406.GF3249@paulmck-ThinkPad-P72> <20201113175754.GA6273@paulmck-ThinkPad-P72> <20201117105236.GA1964407@elver.google.com> <20201117182915.GM1437@paulmck-ThinkPad-P72> <20201118225621.GA1770130@elver.google.com> <20201118233841.GS1437@paulmck-ThinkPad-P72> <20201119125357.GA2084963@elver.google.com> <20201119151409.GU1437@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="jRHKVT23PllUwdXP" Content-Disposition: inline In-Reply-To: <20201119151409.GU1437@paulmck-ThinkPad-P72> User-Agent: Mutt/1.14.6 (2020-07-11) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --jRHKVT23PllUwdXP Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thu, Nov 19, 2020 at 07:14AM -0800, Paul E. McKenney wrote: > On Thu, Nov 19, 2020 at 01:53:57PM +0100, Marco Elver wrote: > > On Wed, Nov 18, 2020 at 03:38PM -0800, Paul E. McKenney wrote: > > > On Wed, Nov 18, 2020 at 11:56:21PM +0100, Marco Elver wrote: > > > > [...] > > > > I think I figured out one piece of the puzzle. Bisection keeps pointing > > > > me at some -rcu merge commit, which kept throwing me off. Nor did it > > > > help that reproduction is a bit flaky. However, I think there are 2 > > > > independent problems, but the manifestation of 1 problem triggers the > > > > 2nd problem: > > > > > > > > 1. problem: slowed forward progress (workqueue lockup / RCU stall reports) > > > > > > > > 2. problem: DEADLOCK which causes complete system lockup > > > > > > > > | ... > > > > | CPU0 > > > > | ---- > > > > | lock(rcu_node_0); > > > > | > > > > | lock(rcu_node_0); > > > > | > > > > | *** DEADLOCK *** > > > > | > > > > | 1 lock held by event_benchmark/105: > > > > | #0: ffffbb6e0b804458 (rcu_node_0){?.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] > > > > | #0: ffffbb6e0b804458 (rcu_node_0){?.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] > > > > | #0: ffffbb6e0b804458 (rcu_node_0){?.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3752 [inline] > > > > | #0: ffffbb6e0b804458 (rcu_node_0){?.-.}-{2:2}, at: rcu_sched_clock_irq+0x428/0xd40 kernel/rcu/tree.c:2581 > > > > | ... > > > > > > > > Problem 2 can with reasonable confidence (5 trials) be fixed by reverting: > > > > > > > > rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled > > > > > > > > At which point the system always boots to user space -- albeit with a > > > > bunch of warnings still (attached). The supposed "good" version doesn't > > > > end up with all those warnings deterministically, so I couldn't say if > > > > the warnings are expected due to recent changes or not (Arm64 QEMU > > > > emulation, 1 CPU, and lots of debugging tools on). > > > > > > > > Does any of that make sense? > > > > > > Marco, it makes all too much sense! :-/ > > > > > > Does the patch below help? > > > > > > Thanx, Paul > > > > > > ------------------------------------------------------------------------ > > > > > > commit 444ef3bbd0f243b912fdfd51f326704f8ee872bf > > > Author: Peter Zijlstra > > > Date: Sat Aug 29 10:22:24 2020 -0700 > > > > > > sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled > > > > My assumption is that this is a replacement for "rcu: Don't invoke > > try_invoke_on_locked_down_task() with irqs disabled", right? > > Hmmm... It was actually intended to be in addition. > > > That seems to have the same result (same test setup) as only reverting > > "rcu: Don't invoke..." does: still results in a bunch of workqueue > > lockup warnings and RCU stall warnings, but boots to user space. I > > attached a log. If the warnings are expected (are they?), then it looks > > fine to me. > > No, they are not at all expected, but might be a different symptom > of the original problem. Please see below. > > > (And just in case: with "rcu: Don't invoke..." and "sched/core: > > Allow..." both applied I still get DEADLOCKs -- but that's probably > > expected.) > > As noted earlier, it is a surprise. Could you please send me the > console output? I've attached the output of a run with both commits applied. > > Testing all events: OK > > hrtimer: interrupt took 17120368 ns > > Running tests again, along with the function tracer > > Running tests on all trace events: > > Testing all events: > > BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 12s! > > Showing busy workqueues and worker pools: > > workqueue events: flags=0x0 > > pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 > > pending: vmstat_shepherd > > BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 17s! > > Showing busy workqueues and worker pools: > > workqueue events: flags=0x0 > > pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 > > pending: vmstat_shepherd > > workqueue events_power_efficient: flags=0x82 > > pwq 2: cpus=0 flags=0x4 nice=0 active=1/256 refcnt=3 > > pending: neigh_periodic_work > > ------------[ cut here ]------------ > > WARNING: CPU: 0 PID: 1 at kernel/rcu/tree_stall.h:758 rcu_check_gp_start_stall kernel/rcu/tree_stall.h:750 [inline] > > WARNING: CPU: 0 PID: 1 at kernel/rcu/tree_stall.h:758 rcu_check_gp_start_stall.isra.0+0x14c/0x210 kernel/rcu/tree_stall.h:711 > > I have different line numbering, This is still using next-20201110. I'll rerun with latest -next as well. > but the only warning that I see in this > function is the one complaining that RCU has been ignoring a request to > start a grace period for too long. This usually happens because the RCU > grace-period kthread (named "rcu_preempt" in your case, but can also be > named "rcu_sched") is being prevented from running, but can be caused > by other things as well. > > > Modules linked in: > > CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.0-rc3-next-20201110-00003-g920304642405-dirty #30 > > Hardware name: linux,dummy-virt (DT) > > pstate: 20000085 (nzCv daIf -PAN -UAO -TCO BTYPE=--) > > pc : rcu_check_gp_start_stall kernel/rcu/tree_stall.h:750 [inline] > > pc : rcu_check_gp_start_stall.isra.0+0x14c/0x210 kernel/rcu/tree_stall.h:711 > > lr : __xchg_mb arch/arm64/include/asm/cmpxchg.h:88 [inline] > > lr : atomic_xchg include/asm-generic/atomic-instrumented.h:615 [inline] > > lr : rcu_check_gp_start_stall kernel/rcu/tree_stall.h:751 [inline] > > lr : rcu_check_gp_start_stall.isra.0+0x148/0x210 kernel/rcu/tree_stall.h:711 > > Two program counters and four link registers? Awesome! ;-) Ah I'm using syzkaller's symbolizer, which duplicates lines if there was an inline function (remove all the "[inline]" and it should make sense, but the "[inline]" tell you the actual line). Obviously for things like this it's a bit unintuitive. :-) > > sp : ffff800010003d20 > > x29: ffff800010003d20 x28: ffff274ac3a10000 > > x27: 0000000000000000 x26: ffff274b3dbe72d8 > > x25: ffffbcb867722000 x24: 0000000000000000 > > x23: 0000000000000000 x22: ffffbcb8681d1260 > > x21: ffffbcb86735b000 x20: ffffbcb867404440 > > x19: ffffbcb867404440 x18: 0000000000000123 > > x17: ffffbcb865d400f0 x16: 0000000000000002 > > x15: 0000000000000002 x14: 0000000000000000 > > x13: 003d090000000000 x12: 00001e8480000000 > > x11: ffffbcb867958980 x10: ffff800010003cf0 > > x9 : ffffbcb864f4b7c8 x8 : 0000000000000080 > > x7 : 0000000000000026 x6 : ffffbcb86774e4c0 > > x5 : 0000000000000000 x4 : 00000000d4001f4b > > x3 : 0000000000000000 x2 : 0000000000000000 > > x1 : 0000000000000001 x0 : 0000000000000000 > > Call trace: > > rcu_check_gp_start_stall kernel/rcu/tree_stall.h:750 [inline] > > rcu_check_gp_start_stall.isra.0+0x14c/0x210 kernel/rcu/tree_stall.h:711 > > rcu_core+0x168/0x9e0 kernel/rcu/tree.c:2719 > > rcu_core_si+0x18/0x28 kernel/rcu/tree.c:2737 > > The RCU_SOFTIRQ handler is causing this checking to occur, for whatever > that is worth. > > > __do_softirq+0x188/0x6b4 kernel/softirq.c:298 > > do_softirq_own_stack include/linux/interrupt.h:568 [inline] > > invoke_softirq kernel/softirq.c:393 [inline] > > __irq_exit_rcu kernel/softirq.c:423 [inline] > > irq_exit+0x1cc/0x1e0 kernel/softirq.c:447 > > __handle_domain_irq+0xb4/0x130 kernel/irq/irqdesc.c:690 > > handle_domain_irq include/linux/irqdesc.h:170 [inline] > > gic_handle_irq+0x70/0x108 drivers/irqchip/irq-gic.c:370 > > el1_irq+0xc0/0x180 arch/arm64/kernel/entry.S:651 > > arch_local_irq_restore+0x8/0x10 arch/arm64/include/asm/irqflags.h:124 > > release_probes kernel/tracepoint.c:113 [inline] > > tracepoint_remove_func kernel/tracepoint.c:315 [inline] > > tracepoint_probe_unregister+0x220/0x378 kernel/tracepoint.c:382 > > trace_event_reg+0x58/0x150 kernel/trace/trace_events.c:298 > > __ftrace_event_enable_disable+0x424/0x608 kernel/trace/trace_events.c:412 > > ftrace_event_enable_disable kernel/trace/trace_events.c:495 [inline] > > __ftrace_set_clr_event_nolock+0x120/0x180 kernel/trace/trace_events.c:811 > > __ftrace_set_clr_event+0x60/0x90 kernel/trace/trace_events.c:833 > > event_trace_self_tests+0xd4/0x114 kernel/trace/trace_events.c:3661 > > event_trace_self_test_with_function kernel/trace/trace_events.c:3734 [inline] > > event_trace_self_tests_init+0x88/0xa8 kernel/trace/trace_events.c:3747 > > do_one_initcall+0xa4/0x500 init/main.c:1212 > > do_initcall_level init/main.c:1285 [inline] > > do_initcalls init/main.c:1301 [inline] > > do_basic_setup init/main.c:1321 [inline] > > kernel_init_freeable+0x344/0x3c4 init/main.c:1521 > > kernel_init+0x20/0x16c init/main.c:1410 > > ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 > > irq event stamp: 3274113 > > hardirqs last enabled at (3274112): [] rcu_core+0x974/0x9e0 kernel/rcu/tree.c:2716 > > hardirqs last disabled at (3274113): [] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline] > > hardirqs last disabled at (3274113): [] _raw_spin_lock_irqsave+0xb8/0x14c kernel/locking/spinlock.c:159 > > softirqs last enabled at (3272576): [] __do_softirq+0x630/0x6b4 kernel/softirq.c:325 > > softirqs last disabled at (3274101): [] do_softirq_own_stack include/linux/interrupt.h:568 [inline] > > softirqs last disabled at (3274101): [] invoke_softirq kernel/softirq.c:393 [inline] > > softirqs last disabled at (3274101): [] __irq_exit_rcu kernel/softirq.c:423 [inline] > > softirqs last disabled at (3274101): [] irq_exit+0x1cc/0x1e0 kernel/softirq.c:447 > > ---[ end trace 902768efebf5a607 ]--- > > rcu: rcu_preempt: wait state: RCU_GP_WAIT_GPS(1) ->state: 0x0 delta ->gp_activity 4452 ->gp_req_activity 3848 ->gp_wake_time 3848 ->gp_wake_seq 2696 ->gp_seq 2696 ->gp_seq_needed 2700 ->gp_flags 0x1 > > The last thing that RCU's grace-period kthread did was to go to sleep > waiting for a grace-period request (RCU_GP_WAIT_GPS). > > > rcu: rcu_node 0:0 ->gp_seq 2696 ->gp_seq_needed 2700 > > rcu: RCU callbacks invoked since boot: 2583 > > rcu_tasks: RTGS_WAIT_CBS(11) since 567120 g:1 i:0/0 k. > > rcu_tasks_rude: RTGS_WAIT_CBS(11) since 567155 g:1 i:0/1 k. > > rcu_tasks_trace: RTGS_INIT(0) since 4295464549 g:0 i:0/0 k. N0 h:0/0/0 > > rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: > > (detected by 0, t=3752 jiffies, g=2705, q=8) > > rcu: All QSes seen, last rcu_preempt kthread activity 557 (4295471128-4295470571), jiffies_till_next_fqs=1, root ->qsmask 0x0 > > rcu: rcu_preempt kthread starved for 557 jiffies! g2705 f0x2 RCU_GP_CLEANUP(7) ->state=0x0 ->cpu=0 > > And here we see that RCU's grace-period kthread has in fact been starved. > > This kthread is now in RCU_GP_CLEANUP, perhaps because of the wakeup that is > sent in rcu_check_gp_kthread_starvation(). > > My current guess is that this is a consequence of the earlier failures, > but who knows? I can try bisection again, or reverting some commits that might be suspicious? But we'd need some selection of suspicious commits. Thanks, -- Marco --jRHKVT23PllUwdXP Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename=report Testing all events: OK Running tests again, along with the function tracer Running tests on all trace events: Testing all events: hrtimer: interrupt took 10901376 ns BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 12s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 pending: vmstat_shepherd workqueue events_power_efficient: flags=0x82 pwq 2: cpus=0 flags=0x4 nice=0 active=1/256 refcnt=3 pending: neigh_periodic_work BUG: workqueue lockup - pool cpus=0 flags=0x5 nice=0 stuck for 11s! Showing busy workqueues and worker pools: workqueue events_power_efficient: flags=0x82 pwq 2: cpus=0 flags=0x5 nice=0 active=3/256 refcnt=5 in-flight: 99:check_lifetime pending: neigh_periodic_work, do_cache_clean pool 2: cpus=0 flags=0x5 nice=0 hung=11s workers=2 manager: 61 BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 10s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 pending: vmstat_shepherd workqueue events_power_efficient: flags=0x82 pwq 2: cpus=0 flags=0x4 nice=0 active=1/256 refcnt=3 in-flight: 107:check_lifetime pool 2: cpus=0 flags=0x4 nice=0 hung=8s workers=4 idle: 99 106 61 BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 20s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 pending: vmstat_shepherd workqueue events_power_efficient: flags=0x82 pwq 2: cpus=0 flags=0x4 nice=0 active=1/256 refcnt=3 in-flight: 107:check_lifetime pool 2: cpus=0 flags=0x4 nice=0 hung=2s workers=4 idle: 99 106 61 rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: (detected by 0, t=3752 jiffies, g=2501, q=1) rcu: All QSes seen, last rcu_preempt kthread activity 3472 (4295298049-4295294577), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread starved for 3472 jiffies! g2501 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0 rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior. rcu: RCU grace-period kthread stack dump: task:rcu_preempt state:I stack: 0 pid: 10 ppid: 2 flags:0x0000042a Call trace: dump_backtrace+0x0/0x240 arch/arm64/kernel/stacktrace.c:100 show_stack+0x34/0x88 arch/arm64/kernel/stacktrace.c:196 sched_show_task kernel/sched/core.c:6444 [inline] sched_show_task+0x1fc/0x228 kernel/sched/core.c:6419 rcu_check_gp_kthread_starvation+0xc8/0xe4 kernel/rcu/tree_stall.h:465 print_other_cpu_stall kernel/rcu/tree_stall.h:532 [inline] check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] rcu_pending kernel/rcu/tree.c:3752 [inline] rcu_sched_clock_irq+0xc2c/0xd40 kernel/rcu/tree.c:2581 update_process_times+0x6c/0xb8 kernel/time/timer.c:1709 tick_sched_handle.isra.0+0x58/0x88 kernel/time/tick-sched.c:176 tick_sched_timer+0x68/0xe0 kernel/time/tick-sched.c:1328 __run_hrtimer kernel/time/hrtimer.c:1519 [inline] __hrtimer_run_queues+0x288/0x730 kernel/time/hrtimer.c:1583 hrtimer_interrupt+0x114/0x288 kernel/time/hrtimer.c:1645 timer_handler drivers/clocksource/arm_arch_timer.c:647 [inline] arch_timer_handler_virt+0x50/0x70 drivers/clocksource/arm_arch_timer.c:658 handle_percpu_devid_irq+0x104/0x4c0 kernel/irq/chip.c:930 generic_handle_irq_desc include/linux/irqdesc.h:152 [inline] generic_handle_irq+0x54/0x78 kernel/irq/irqdesc.c:650 __handle_domain_irq+0xac/0x130 kernel/irq/irqdesc.c:687 handle_domain_irq include/linux/irqdesc.h:170 [inline] gic_handle_irq+0x70/0x108 drivers/irqchip/irq-gic.c:370 el1_irq+0xc0/0x180 arch/arm64/kernel/entry.S:651 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:124 [inline] rcu_irq_enter_irqson+0x40/0x78 kernel/rcu/tree.c:1078 trace_preempt_disable_rcuidle include/trace/events/preemptirq.h:51 [inline] trace_preempt_off+0x108/0x1f8 kernel/trace/trace_preemptirq.c:130 preempt_latency_start kernel/sched/core.c:4163 [inline] preempt_latency_start kernel/sched/core.c:4156 [inline] preempt_schedule_common+0x170/0x1a8 kernel/sched/core.c:4679 preempt_schedule+0x38/0x40 kernel/sched/core.c:4705 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline] _raw_spin_unlock_irqrestore+0x90/0xa0 kernel/locking/spinlock.c:191 prepare_to_swait_event+0x84/0xe8 kernel/sched/swait.c:120 rcu_gp_fqs_loop kernel/rcu/tree.c:1942 [inline] rcu_gp_kthread+0x630/0x1bd8 kernel/rcu/tree.c:2115 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 ================================ WARNING: inconsistent lock state 5.10.0-rc3-next-20201110-00003-g891a69a3957e #1 Not tainted -------------------------------- inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. rcu_preempt/10 [HC0[0]:SC0[0]:HE0:SE1] takes: ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3752 [inline] ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: rcu_sched_clock_irq+0x428/0xd40 kernel/rcu/tree.c:2581 {IN-HARDIRQ-W} state was registered at: mark_lock kernel/locking/lockdep.c:4374 [inline] mark_usage kernel/locking/lockdep.c:4302 [inline] __lock_acquire+0xaa8/0x1a50 kernel/locking/lockdep.c:4785 lock_acquire kernel/locking/lockdep.c:5436 [inline] lock_acquire+0x268/0x508 kernel/locking/lockdep.c:5401 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x78/0x14c kernel/locking/spinlock.c:159 print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] rcu_pending kernel/rcu/tree.c:3752 [inline] rcu_sched_clock_irq+0x428/0xd40 kernel/rcu/tree.c:2581 update_process_times+0x6c/0xb8 kernel/time/timer.c:1709 tick_sched_handle.isra.0+0x58/0x88 kernel/time/tick-sched.c:176 tick_sched_timer+0x68/0xe0 kernel/time/tick-sched.c:1328 __run_hrtimer kernel/time/hrtimer.c:1519 [inline] __hrtimer_run_queues+0x288/0x730 kernel/time/hrtimer.c:1583 hrtimer_interrupt+0x114/0x288 kernel/time/hrtimer.c:1645 timer_handler drivers/clocksource/arm_arch_timer.c:647 [inline] arch_timer_handler_virt+0x50/0x70 drivers/clocksource/arm_arch_timer.c:658 handle_percpu_devid_irq+0x104/0x4c0 kernel/irq/chip.c:930 generic_handle_irq_desc include/linux/irqdesc.h:152 [inline] generic_handle_irq+0x54/0x78 kernel/irq/irqdesc.c:650 __handle_domain_irq+0xac/0x130 kernel/irq/irqdesc.c:687 handle_domain_irq include/linux/irqdesc.h:170 [inline] gic_handle_irq+0x70/0x108 drivers/irqchip/irq-gic.c:370 el1_irq+0xc0/0x180 arch/arm64/kernel/entry.S:651 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:124 [inline] rcu_irq_enter_irqson+0x40/0x78 kernel/rcu/tree.c:1078 trace_preempt_disable_rcuidle include/trace/events/preemptirq.h:51 [inline] trace_preempt_off+0x108/0x1f8 kernel/trace/trace_preemptirq.c:130 preempt_latency_start kernel/sched/core.c:4163 [inline] preempt_latency_start kernel/sched/core.c:4156 [inline] preempt_schedule_common+0x170/0x1a8 kernel/sched/core.c:4679 preempt_schedule+0x38/0x40 kernel/sched/core.c:4705 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline] _raw_spin_unlock_irqrestore+0x90/0xa0 kernel/locking/spinlock.c:191 prepare_to_swait_event+0x84/0xe8 kernel/sched/swait.c:120 rcu_gp_fqs_loop kernel/rcu/tree.c:1942 [inline] rcu_gp_kthread+0x630/0x1bd8 kernel/rcu/tree.c:2115 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 irq event stamp: 43978 hardirqs last enabled at (43977): [] rcu_irq_enter_irqson+0x64/0x78 kernel/rcu/tree.c:1078 hardirqs last disabled at (43978): [] el1_irq+0x80/0x180 arch/arm64/kernel/entry.S:648 softirqs last enabled at (43682): [] __do_softirq+0x630/0x6b4 kernel/softirq.c:325 softirqs last disabled at (43673): [] do_softirq_own_stack include/linux/interrupt.h:568 [inline] softirqs last disabled at (43673): [] invoke_softirq kernel/softirq.c:393 [inline] softirqs last disabled at (43673): [] __irq_exit_rcu kernel/softirq.c:423 [inline] softirqs last disabled at (43673): [] irq_exit+0x1cc/0x1e0 kernel/softirq.c:447 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(rcu_node_0); lock(rcu_node_0); *** DEADLOCK *** 1 lock held by rcu_preempt/10: #0: ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] #0: ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] #0: ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3752 [inline] #0: ffffb80c721e4458 (rcu_node_0){?.-.}-{2:2}, at: rcu_sched_clock_irq+0x428/0xd40 kernel/rcu/tree.c:2581 stack backtrace: CPU: 0 PID: 10 Comm: rcu_preempt Not tainted 5.10.0-rc3-next-20201110-00003-g891a69a3957e #1 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x240 arch/arm64/kernel/stacktrace.c:100 show_stack+0x34/0x88 arch/arm64/kernel/stacktrace.c:196 __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x140/0x1bc lib/dump_stack.c:118 print_usage_bug kernel/locking/lockdep.c:3739 [inline] print_usage_bug+0x2a0/0x2f0 kernel/locking/lockdep.c:3706 valid_state kernel/locking/lockdep.c:3750 [inline] mark_lock_irq kernel/locking/lockdep.c:3953 [inline] mark_lock.part.0+0x438/0x4e8 kernel/locking/lockdep.c:4410 mark_lock kernel/locking/lockdep.c:4008 [inline] mark_held_locks+0x54/0x90 kernel/locking/lockdep.c:4011 __trace_hardirqs_on_caller kernel/locking/lockdep.c:4029 [inline] lockdep_hardirqs_on_prepare+0xe0/0x290 kernel/locking/lockdep.c:4097 trace_hardirqs_on+0x90/0x370 kernel/trace/trace_preemptirq.c:49 el1_irq+0xdc/0x180 arch/arm64/kernel/entry.S:685 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:124 [inline] rcu_irq_enter_irqson+0x40/0x78 kernel/rcu/tree.c:1078 trace_preempt_disable_rcuidle include/trace/events/preemptirq.h:51 [inline] trace_preempt_off+0x108/0x1f8 kernel/trace/trace_preemptirq.c:130 preempt_latency_start kernel/sched/core.c:4163 [inline] preempt_latency_start kernel/sched/core.c:4156 [inline] preempt_schedule_common+0x170/0x1a8 kernel/sched/core.c:4679 preempt_schedule+0x38/0x40 kernel/sched/core.c:4705 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline] _raw_spin_unlock_irqrestore+0x90/0xa0 kernel/locking/spinlock.c:191 prepare_to_swait_event+0x84/0xe8 kernel/sched/swait.c:120 rcu_gp_fqs_loop kernel/rcu/tree.c:1942 [inline] rcu_gp_kthread+0x630/0x1bd8 kernel/rcu/tree.c:2115 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 BUG: scheduling while atomic: rcu_preempt/10/0x00000002 INFO: lockdep is turned off. Modules linked in: Preemption disabled at: [] preempt_schedule+0x38/0x40 kernel/sched/core.c:4705 CPU: 0 PID: 10 Comm: rcu_preempt Not tainted 5.10.0-rc3-next-20201110-00003-g891a69a3957e #1 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x240 arch/arm64/kernel/stacktrace.c:100 show_stack+0x34/0x88 arch/arm64/kernel/stacktrace.c:196 __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x140/0x1bc lib/dump_stack.c:118 __schedule_bug+0xcc/0xe0 kernel/sched/core.c:4261 schedule_debug kernel/sched/core.c:4288 [inline] __schedule+0x888/0x970 kernel/sched/core.c:4416 preempt_schedule_common+0x4c/0x1a8 kernel/sched/core.c:4680 preempt_schedule+0x38/0x40 kernel/sched/core.c:4705 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline] _raw_spin_unlock_irqrestore+0x90/0xa0 kernel/locking/spinlock.c:191 prepare_to_swait_event+0x84/0xe8 kernel/sched/swait.c:120 rcu_gp_fqs_loop kernel/rcu/tree.c:1942 [inline] rcu_gp_kthread+0x630/0x1bd8 kernel/rcu/tree.c:2115 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 --jRHKVT23PllUwdXP--