Re: linux-next: Tree for Aug 26

From: Paul E. McKenney
Date: Wed Aug 26 2020 - 15:39:55 EST

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On Wed, Aug 26, 2020 at 08:19:01PM +0200, Anders Roxell wrote:
> On Wed, 26 Aug 2020 at 08:33, Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:

[ . . . ]

> I've built and run an arm64 allmodconfig kernel where I use the
> defconfig as the base, I do this for testing purposes.
> I can see the following call trace [1]:
>
> [ 2595.811453][ T1] Running tests on all trace events:
> [ 2595.860933][ T1] Testing all events:
> [ 4316.066072][ T8] kworker/dying (8) used greatest stack depth:
> 27056 bytes left
> [ 8561.924871][ C0] watchdog: BUG: soft lockup - CPU#0 stuck for
> 22s! [migration/0:14]
> [ 8561.934498][ C0] Modules linked in:
> [ 8561.942303][ C0] irq event stamp: 4044
> [ 8561.949044][ C0] hardirqs last enabled at (4043):
> [<ffffa000126b530c>] _raw_spin_unlock_irqrestore+0xac/0x138
> [ 8561.960848][ C0] hardirqs last disabled at (4044):
> [<ffffa000126a89f8>] __schedule+0xf8/0x7e0
> [ 8561.971418][ C0] softirqs last enabled at (3698):
> [<ffffa00010001b04>] __do_softirq+0x524/0x5f8
> [ 8561.982191][ C0] softirqs last disabled at (3689):
> [<ffffa000101216c8>] __irq_exit_rcu+0x128/0x1a0
> [ 8561.993068][ C0] CPU: 0 PID: 14 Comm: migration/0 Tainted: G
> W 5.9.0-rc2-next-20200826-00005-g24628bb4c0bf #1
> [ 8562.005684][ C0] Hardware name: linux,dummy-virt (DT)
> [ 8562.013247][ C0] pstate: 80400005 (Nzcv daif +PAN -UAO BTYPE=--)
> [ 8562.021657][ C0] pc : arch_local_irq_enable+0x58/0x80
> [ 8562.029323][ C0] lr : _raw_spin_unlock_irq+0x84/0xc0
> [ 8562.036739][ C0] sp : ffff0000698efaa0
> [ 8562.042984][ C0] x29: ffff0000698efaa0 x28: ffff00006ad0f270
> [ 8562.053814][ C0] x27: ffff00006ad0f248 x26: ffff0000698d4718
> [ 8562.064687][ C0] x25: ffff00006ad0e798 x24: ffffa000139e3a40
> [ 8562.075506][ C0] x23: 0000000000000001 x22: ffffa000154f5000
> [ 8562.086425][ C0] x21: ffff00006ad0e798 x20: ffff00006ad0e780
> [ 8562.097255][ C0] x19: ffffa000126a905c x18: 00000000000014c0
> [ 8562.108071][ C0] x17: 0000000000001500 x16: 0000000000001440
> [ 8562.118918][ C0] x15: 00000000f1f1f1f1 x14: 003d090000000000
> [ 8562.129739][ C0] x13: 00003d0900000000 x12: ffff80000d31df41
> [ 8562.140544][ C0] x11: 1fffe0000d31df40 x10: ffff80000d31df40
> [ 8562.151366][ C0] x9 : dfffa00000000000 x8 : ffff0000698efa07
> [ 8562.162247][ C0] x7 : 0000000000000001 x6 : 00007ffff2ce20c0
> [ 8562.173072][ C0] x5 : ffff0000698d4040 x4 : dfffa00000000000
> [ 8562.183954][ C0] x3 : ffffa0001040f904 x2 : 0000000000000007
> [ 8562.194811][ C0] x1 : ffffa00014080000 x0 : 00000000000000e0
> [ 8562.205858][ C0] Call trace:
> [ 8562.211739][ C0] arch_local_irq_enable+0x58/0x80
> [ 8562.219076][ C0] _raw_spin_unlock_irq+0x84/0xc0
> [ 8562.226394][ C0] __schedule+0x75c/0x7e0
> [ 8562.233074][ C0] preempt_schedule_notrace+0x64/0xc0
> [ 8562.268210][ C0] ftrace_ops_list_func+0x494/0x4e0
> [ 8562.275735][ C0] ftrace_graph_call+0x0/0x4
> [ 8562.282647][ C0] preempt_count_add+0xc/0x240
> [ 8562.289686][ C0] schedule+0xe4/0x160
> [ 8562.296187][ C0] smpboot_thread_fn+0x47c/0x540
> [ 8562.303377][ C0] kthread+0x23c/0x260
> [ 8562.309906][ C0] ret_from_fork+0x10/0x18
> [ 8562.316604][ C0] Kernel panic - not syncing: softlockup: hung tasks
> [ 8562.325230][ C0] CPU: 0 PID: 14 Comm: migration/0 Tainted: G
> W L 5.9.0-rc2-next-20200826-00005-g24628bb4c0bf #1
> [ 8562.337861][ C0] Hardware name: linux,dummy-virt (DT)
> [ 8562.345374][ C0] Call trace:
> [ 8562.351228][ C0] dump_backtrace+0x0/0x320
> [ 8562.358070][ C0] show_stack+0x38/0x60
> [ 8562.364728][ C0] dump_stack+0x1c0/0x280
> [ 8562.371447][ C0] panic+0x32c/0x614
> [ 8562.377868][ C0] watchdog_timer_fn+0x49c/0x560
> [ 8562.385076][ C0] __run_hrtimer+0x1cc/0x360
> [ 8562.392021][ C0] __hrtimer_run_queues+0x1a0/0x220
> [ 8562.399500][ C0] hrtimer_interrupt+0x1f8/0x440
> [ 8562.406807][ C0] arch_timer_handler_virt+0x68/0xa0
> [ 8562.414338][ C0] handle_percpu_devid_irq+0x118/0x2a0
> [ 8562.421992][ C0] __handle_domain_irq+0x150/0x1c0
> [ 8562.429315][ C0] gic_handle_irq+0x98/0x120
> [ 8562.436297][ C0] el1_irq+0xd4/0x1c0

We appear to have taken an interrupt here, just after releasing
an irq-disabled lock and enabling interrupts.

> [ 8562.442748][ C0] arch_local_irq_enable+0x58/0x80
> [ 8562.450116][ C0] _raw_spin_unlock_irq+0x84/0xc0
> [ 8562.457360][ C0] __schedule+0x75c/0x7e0
> [ 8562.464142][ C0] preempt_schedule_notrace+0x64/0xc0
> [ 8562.471745][ C0] ftrace_ops_list_func+0x494/0x4e0
> [ 8562.479195][ C0] ftrace_graph_call+0x0/0x4
> [ 8562.486159][ C0] preempt_count_add+0xc/0x240
> [ 8562.493210][ C0] schedule+0xe4/0x160

We are trying to sleep, so we took a pass through the scheduler and
did some tracing.

> [ 8562.499737][ C0] smpboot_thread_fn+0x47c/0x540

Here we might be bringing up a CPU? Except that according to your
dmesg, there is only one CPU. ("RCU restricting CPUs from NR_CPUS=256
to nr_cpu_ids=1"). So this seems unlikely.

Huh. The first dmesg in output-next-20200826.log is instead a
DEBUG_LOCKS_WARN_ON() from lockdep. Might this be related? Or do you
also see this warning when boot happens quickly?

(I do see the soft lockup later on.)

> [ 8562.506960][ C0] kthread+0x23c/0x260
> [ 8562.513496][ C0] ret_from_fork+0x10/0x18
> [ 8562.521052][ C0] Kernel Offset: disabled
> [ 8562.527725][ C0] CPU features: 0x0240002,20002004
> [ 8562.534950][ C0] Memory Limit: none
> [ 8562.543830][ C0] ---[ end Kernel panic - not syncing:
> softlockup: hung tasks ]---
>
> When I tested to checkout and build e6df9766894d ("Merge remote-tracking branch
> 'irqchip/irq/irqchip-next' into master") that was merged into today's
> tag I was able to
> boot [2]. When I checked out 25e6e115dd1d ("Merge remote-tracking
> branch 'rcu/rcu/next' into master") and built and tested that I was
> able to boot [3] after a
> looong time. To clarify, the rcu merge comes after the irqchip merge.
>
> I also tried to only revert the rcu tree from todays next tag like this:
> "git diff e6df9766894d..25e6e115dd1d | patch -Rp1". When I built that
> I was able to
> boot [4] too.
>
> Any idea what's going on here?

Could you please try bisecting the RCU commits? They are linear,
extending from 0d23eddbe5d4 ("rcu: Remove KCSAN stubs") to 72cc80705122
("rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp()".

I do regularly test single-CPU premptible RCU, but not on ARM. Nor do
I normally enable quite this much debug, so I might have missed something.

Thanx, Paul

> Cheers,
> Anders
> [1] https://people.linaro.org/~anders.roxell/output-next-20200826.log
> [2] https://people.linaro.org/~anders.roxell/output-next-20200826-bisect-e6df9766894d.log
> [3] https://people.linaro.org/~anders.roxell/output-next-20200826-bisect-25e6e115dd1d.log
> [4] https://people.linaro.org/~anders.roxell/output-next-20200826-bisect-revert-e6df9766894d-25e6e115dd1d.log

Next message: Kees Cook: "Re: [PATCH v4 0/3] io_uring: add restrictions to support untrusted applications and guests"
Previous message: Andy Shevchenko: "Re: [PATCH 02/24] Input: gpio_keys - Simplify with dev_err_probe()"
In reply to: Anders Roxell: "Re: linux-next: Tree for Aug 26"
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