From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1, USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 75A2CC5519F for ; Wed, 18 Nov 2020 22:56:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E35ED246EA for ; Wed, 18 Nov 2020 22:56:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="vox9ADdo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725948AbgKRW4O (ORCPT ); Wed, 18 Nov 2020 17:56:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33122 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725710AbgKRW4N (ORCPT ); Wed, 18 Nov 2020 17:56:13 -0500 Received: from mail-wm1-x343.google.com (mail-wm1-x343.google.com [IPv6:2a00:1450:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D910FC0613D4 for ; Wed, 18 Nov 2020 14:56:30 -0800 (PST) Received: by mail-wm1-x343.google.com with SMTP id w24so4608258wmi.0 for ; Wed, 18 Nov 2020 14:56:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=1seX92mFsrfx7vZyLIxprFubCVzfCSOLsu/hjAP+vTs=; b=vox9ADdoLllhyA1WukaU1CRn9MH5Ac1e19bK2BhUq0VExU/Wmxkt8mbTE+40y/r1MV NmZpUniroixmZ0iwh6+lKHnnOBGKRU4uv25M9W9AU7/cgxZ1SuqdFPihrQQnjQzbgznF sE2K77SL8EQpM0acGAMkBG9BZay0+eqqATgSlTrda7OnH697vk4AGc3DJ4iDuygQhF8C s841mg/agEyleLOBAFzE+8WMmLehdkndMmJwA9hfPmP2Vg1sbnpbe91pll7ImLk74dAS JXpP0Jf3cwN9Yh/JEdNPZgB/6srsMK5CcUc+PZTIPurEBsKMKSPWR9q7CYfFDe/oGpoQ ngPg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=1seX92mFsrfx7vZyLIxprFubCVzfCSOLsu/hjAP+vTs=; b=EBeuHvxskI1c2Q7Bml6OX/4abXyOkfJ3GYUCfAcNFGiUJE/QKU3x8qLfRIL3a5pcWH YLi/EAhExd0YCetNp2b3evpjQpSHtSSbsstUOS9irDEn0ia2ZnoMsitAlvL/eMJeVoJk wc8pOceCkZdLr/UNeh4GWLe6vzskPyy9GAZWWRs5OgAKmIzWVu84dayixJHH5qN0uns8 xTflyJXN6Geg1dl7bzie7DemcwOjsNKH8qqUL10MoLRFnPfVvIJj9G0bHiBfPu0lisMG MgbBnWzud7fbF6oqyg2cUSEf5MvHj9mdglUBcKXl9C+RUNQKjXAY0cixywyPpR0jPAkB svTQ== X-Gm-Message-State: AOAM532tNiSRJRbmMPqzqOaW7KgUgdiyjNOn3YJ/Ih6xi6xWtWtfcL3C +J9a2NDQF5CjXAkU1VDS1NqZmQ== X-Google-Smtp-Source: ABdhPJwdlAxRq7xNFMtlK6ne5yf2WkyW7uJ1VlCtr6keEqO7/0WNjQ19rvEqd/QRHs2EefbueKWGMw== X-Received: by 2002:a7b:cc84:: with SMTP id p4mr1406309wma.86.1605740189466; Wed, 18 Nov 2020 14:56:29 -0800 (PST) Received: from elver.google.com ([2a00:79e0:15:13:f693:9fff:fef4:2449]) by smtp.gmail.com with ESMTPSA id p4sm35980145wrm.51.2020.11.18.14.56.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Nov 2020 14:56:27 -0800 (PST) Date: Wed, 18 Nov 2020 23:56:21 +0100 From: Marco Elver To: "Paul E. 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: <20201118225621.GA1770130@elver.google.com> References: <20201111183430.GN517454@elver.google.com> <20201111192123.GB3249@paulmck-ThinkPad-P72> <20201111202153.GT517454@elver.google.com> <20201112001129.GD3249@paulmck-ThinkPad-P72> <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> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="0OAP2g/MAC+5xKAE" Content-Disposition: inline In-Reply-To: <20201117182915.GM1437@paulmck-ThinkPad-P72> User-Agent: Mutt/1.14.6 (2020-07-11) Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org --0OAP2g/MAC+5xKAE Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Nov 17, 2020 at 10:29AM -0800, Paul E. McKenney wrote: [...] > But it would be good to get the kcompactd() people to look at this (not > immediately seeing who they are in MAINTAINERS). Perhaps preemption is > disabled somehow and I am failing to see it. > > Failing that, maybe someone knows of a way to check for overly long > timeout handlers. 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? Thanks, -- Marco --0OAP2g/MAC+5xKAE Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename=log Testing all events: OK Running tests again, along with the function tracer Running tests on all trace events: Testing all events: hrtimer: interrupt took 10156432 ns rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: (detected by 0, t=3752 jiffies, g=2785, q=6) rcu: All QSes seen, last rcu_preempt kthread activity 3752 (4295396561-4295392809), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread starved for 3752 jiffies! g2785 f0x0 RCU_GP_ONOFF(3) ->state=0x0 ->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:R running task stack: 0 pid: 10 ppid: 2 flags:0x00000428 Call trace: __switch_to+0x10c/0x200 arch/arm64/kernel/process.c:578 context_switch kernel/sched/core.c:3773 [inline] __schedule+0x2d8/0x980 kernel/sched/core.c:4522 preempt_schedule_common+0x4c/0x1a8 kernel/sched/core.c:4681 preempt_schedule+0x38/0x40 kernel/sched/core.c:4706 __raw_spin_unlock include/linux/spinlock_api_smp.h:152 [inline] _raw_spin_unlock+0x94/0xa8 kernel/locking/spinlock.c:183 rcu_gp_init kernel/rcu/tree.c:1820 [inline] rcu_gp_kthread+0x34c/0x1bd8 kernel/rcu/tree.c:2105 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: (detected by 0, t=3752 jiffies, g=2817, q=6) rcu: All QSes seen, last rcu_preempt kthread activity 856 (4295412565-4295411709), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread starved for 856 jiffies! g2817 f0x2 RCU_GP_CLEANUP(7) ->state=0x0 ->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:R running task stack: 0 pid: 10 ppid: 2 flags:0x00000428 Call trace: __switch_to+0x10c/0x200 arch/arm64/kernel/process.c:578 context_switch kernel/sched/core.c:3773 [inline] __schedule+0x2d8/0x980 kernel/sched/core.c:4522 preempt_schedule_common+0x4c/0x1a8 kernel/sched/core.c:4681 preempt_schedule+0x38/0x40 kernel/sched/core.c:4706 __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline] _raw_spin_unlock_irq+0x84/0x98 kernel/locking/spinlock.c:199 rcu_gp_cleanup kernel/rcu/tree.c:2015 [inline] rcu_gp_kthread+0x1038/0x1bd8 kernel/rcu/tree.c:2119 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 BUG: workqueue lockup - pool cpus=0 flags=0x4 nice=0 stuck for 16s! 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=2/256 refcnt=4 pending: neigh_periodic_work, do_cache_clean workqueue rcu_gp: flags=0x8 pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 in-flight: 15:srcu_invoke_callbacks pool 0: cpus=0 node=0 flags=0x0 nice=0 hung=0s workers=3 idle: 111 5 rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: (detected by 0, t=3752 jiffies, g=2829, q=6) rcu: All QSes seen, last rcu_preempt kthread activity 1522 (4295422970-4295421448), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread starved for 1522 jiffies! g2829 f0x2 RCU_GP_CLEANUP(7) ->state=0x0 ->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:R running task stack: 0 pid: 10 ppid: 2 flags:0x00000428 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:6445 [inline] sched_show_task+0x1fc/0x228 kernel/sched/core.c:6420 rcu_check_gp_kthread_starvation+0xc8/0xe4 kernel/rcu/tree_stall.h:452 print_other_cpu_stall kernel/rcu/tree_stall.h:520 [inline] check_cpu_stall kernel/rcu/tree_stall.h:640 [inline] rcu_pending kernel/rcu/tree.c:3752 [inline] rcu_sched_clock_irq+0xb34/0xc48 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_enable arch/arm64/include/asm/irqflags.h:37 [inline] __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:168 [inline] _raw_spin_unlock_irq+0x50/0x98 kernel/locking/spinlock.c:199 finish_lock_switch kernel/sched/core.c:3513 [inline] finish_task_switch+0xa8/0x290 kernel/sched/core.c:3613 context_switch kernel/sched/core.c:3776 [inline] __schedule+0x2dc/0x980 kernel/sched/core.c:4522 preempt_schedule_common+0x4c/0x1a8 kernel/sched/core.c:4681 preempt_schedule+0x38/0x40 kernel/sched/core.c:4706 __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline] _raw_spin_unlock_irq+0x84/0x98 kernel/locking/spinlock.c:199 rcu_gp_cleanup kernel/rcu/tree.c:2046 [inline] rcu_gp_kthread+0x1144/0x1bd8 kernel/rcu/tree.c:2119 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: (detected by 0, t=3752 jiffies, g=2845, q=6) rcu: All QSes seen, last rcu_preempt kthread activity 2796 (4295435367-4295432571), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread starved for 2796 jiffies! g2845 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->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:R running task 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:6445 [inline] sched_show_task+0x1fc/0x228 kernel/sched/core.c:6420 rcu_check_gp_kthread_starvation+0xc8/0xe4 kernel/rcu/tree_stall.h:452 print_other_cpu_stall kernel/rcu/tree_stall.h:520 [inline] check_cpu_stall kernel/rcu/tree_stall.h:640 [inline] rcu_pending kernel/rcu/tree.c:3752 [inline] rcu_sched_clock_irq+0xb34/0xc48 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:4164 [inline] preempt_latency_start kernel/sched/core.c:4157 [inline] preempt_schedule_notrace+0x170/0x1c0 kernel/sched/core.c:4747 __ftrace_ops_list_func kernel/trace/ftrace.c:6956 [inline] ftrace_ops_list_func+0x108/0x230 kernel/trace/ftrace.c:6977 ftrace_graph_call+0x0/0x4 preempt_count_add+0x8/0x1a0 arch/arm64/include/asm/atomic.h:65 schedule+0x44/0x100 kernel/sched/core.c:4599 schedule_timeout+0x240/0x538 kernel/time/timer.c:1871 rcu_gp_fqs_loop kernel/rcu/tree.c:1942 [inline] rcu_gp_kthread+0x618/0x1bd8 kernel/rcu/tree.c:2115 kthread+0x13c/0x188 kernel/kthread.c:292 ret_from_fork+0x10/0x34 arch/arm64/kernel/entry.S:961 OK --0OAP2g/MAC+5xKAE--