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Date:   Thu, 19 Nov 2020 13:53:57 +0100
From:   Marco Elver <elver@google.com>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Anders Roxell <anders.roxell@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Jann Horn <jannh@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        kasan-dev <kasan-dev@googlegroups.com>, rcu@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Tejun Heo <tj@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH] kfence: Avoid stalling work queue task without
 allocations
Message-ID: <20201119125357.GA2084963@elver.google.com>
References: <20201111202153.GT517454@elver.google.com>
 <20201112001129.GD3249@paulmck-ThinkPad-P72>
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 <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>
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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);
> > 	|   <Interrupt>
> > 	|     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 <peterz@infradead.org>
> 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?

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.

(And just in case: with "rcu: Don't invoke..." and "sched/core:
Allow..." both applied I still get DEADLOCKs -- but that's probably
expected.)

Thanks,
-- Marco

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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
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
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
 __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): [<ffffbcb864f8aee4>] rcu_core+0x974/0x9e0 kernel/rcu/tree.c:2716
hardirqs last disabled at (3274113): [<ffffbcb866233bf0>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (3274113): [<ffffbcb866233bf0>] _raw_spin_lock_irqsave+0xb8/0x14c kernel/locking/spinlock.c:159
softirqs last  enabled at (3272576): [<ffffbcb864e10b80>] __do_softirq+0x630/0x6b4 kernel/softirq.c:325
softirqs last disabled at (3274101): [<ffffbcb864ec6c54>] do_softirq_own_stack include/linux/interrupt.h:568 [inline]
softirqs last disabled at (3274101): [<ffffbcb864ec6c54>] invoke_softirq kernel/softirq.c:393 [inline]
softirqs last disabled at (3274101): [<ffffbcb864ec6c54>] __irq_exit_rcu kernel/softirq.c:423 [inline]
softirqs last disabled at (3274101): [<ffffbcb864ec6c54>] 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
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
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:3772 [inline]
 __schedule+0x2d8/0x980 kernel/sched/core.c:4521
 preempt_schedule_common+0x4c/0x1a8 kernel/sched/core.c:4680
 preempt_schedule+0x38/0x40 kernel/sched/core.c:4705
 __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
OK
Testing ftrace filter: OK
Loading compiled-in X.509 certificates
input: gpio-keys as /devices/platform/gpio-keys/input/input0
ALSA device list:
  No soundcards found.
TAP version 14
1..0
uart-pl011 9000000.pl011: no DMA platform data
EXT4-fs (sda): mounting ext3 file system using the ext4 subsystem
EXT4-fs (sda): mounted filesystem with ordered data mode. Opts: (null)
VFS: Mounted root (ext3 filesystem) readonly on device 8:0.
devtmpfs: mounted
Freeing unused kernel memory: 8832K
Run /sbin/init as init process

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