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SubjectRe: stop_machine() soft lockup
On Wed, Sep 05, 2018 at 10:42:41AM +0200, Peter Zijlstra wrote:
> On Tue, Sep 04, 2018 at 09:03:22PM +0200, Niklas Cassel wrote:
> > Hello Peter,
> >
> > I'm seeing some lockups when booting linux-next on a db820c arm64 board.
> > I've tried to analyze, but I'm currently stuck.
>
> Please see (should be in your Inbox too):
>
> https://lkml.kernel.org/r/20180905084158.GR24124@hirez.programming.kicks-ass.net

I'm sorry if I mislead you by replying to your other mail thread,
both of them have timekeeping_notify() in the call trace,
but my problem has this call trace:

[ 128.747853] wait_for_common+0xe0/0x1a0
[ 128.752023] wait_for_completionx+0x28/0x38
[ 128.755677] __stop_cpus+0xd4/0xf8
[ 128.759837] stop_cpus+0x70/0xa8
[ 128.762958] stop_machine_cpuslocked+0x124/0x130
[ 128.766345] stop_machine+0x54/0x70
[ 128.771373] timekeeping_notify+0x44/0x70
[ 128.774158] __clocksource_select+0xa8/0x1d8
[ 128.778605] clocksource_done_booting+0x4c/0x64
[ 128.782931] do_one_initcall+0x94/0x3f8
[ 128.786921] kernel_init_freeable+0x47c/0x528
[ 128.790742] kernel_init+0x18/0x110
[ 128.795673] ret_from_fork+0x10/0x1c


while your other mail thread has this call trace:

* stop_machine()
* timekeeping_notify()
* __clocksource_select()
* clocksource_select()
* clocksource_watchdog_work()


So my problem is not related to the watchdog, I tried your revert anyway,
but unfortunately my problem persists.


In my problem, what appears to happen is that in the end of multi_cpu_stop(),
local_irq_restore() is called, and an irq comes directly after that,
then after 22 seconds soft lockup detector kicks in (so I appear to still
get timer ticks). The PC that the soft lockup detector prints is the line
after local_irq_restore(). Without any prints, that is simply end brace of
the function.

I'm booting with kernel command line: "earlycon ftrace=irqsoff"
I can't seem to reproduce the problem without ftrace=irqsoff,
not sure if it because of timing or because ftrace is involved.

I managed to get another call trace with ftrace included,
unfortunately both CPUs appear to be printing at the same time.

[ 32.703910] watchdog: BUG: soft lockup - CPU#2 stuck for 22s! [migration/2:22]
[ 32.728589] Modules linked in:
[ 32.747176] irq event stamp: 154
[ 32.758851] hardirqs last enabled at (153): [<ffff0000081bb59c>] multi_cpu_stop+0xfc/0x168
[ 32.770736] hardirqs last disabled at (154): [<ffff000008083e2c>] el1_irq+0xac/0x198
[ 32.774911] watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [kworker/3:0H:30]
[ 32.779946] Modules linked in:
[ 32.786425] softirqs last enabled at (114): [<ffff000008082164>] __do_softirq+0x47c/0x574
[ 32.795450] irq event stamp: 62
[ 32.805549] softirqs last disabled at (95): [<ffff0000080ca41c>] irq_exit+0x134/0x148
[ 32.810450] hardirqs last enabled at (61): [<ffff00000908efe8>] _raw_spin_unlock_irq+0x38/0x78
[ 32.816075] hardirqs last disabled at (62): [<ffff000008083e2c>] el1_irq+0xac/0x198
[ 32.821812] softirqs last enabled at (0): [<ffff0000080bdb68>] copy_process.isra.5.part.6+0x338/0x1ac$
[ 32.829394] CPU: 2 PID: 22 Comm: migration/2 Tainted: G W 4.19.0-rc2-next-20180904-0000$
-gd2e5ea917660 #47
[ 32.836772] softirqs last disabled at (0): [<0000000000000000>] (null)
[ 32.846193] Hardware name: Qualcomm Technologies, Inc. DB820c (DT)
[ 32.857546] CPU: 3 PID: 30 Comm: kworker/3:0H Tainted: G W 4.19.0-rc2-next-20180904-000$
2-gd2e5ea917660 #47
[ 32.864532] pstate: 60400005 (nZCv daif +PAN -UAO)
[ 32.870789] Hardware name: Qualcomm Technologies, Inc. DB820c (DT)
[ 32.881909] pc : multi_cpu_stop+0x100/0x168
[ 32.887583] lr : multi_cpu_stop+0xfc/0x168
[ 32.892723] sp : ffff00000ae33d70
[ 32.897717] x29: ffff00000ae33d70 x28: 0000000000000000
[ 32.906981] pstate: 60400005 (nZCv daif +PAN -UAO)
[ 32.916202] x27: 0000000000000002 x26: ffff00000803bc80
[ 32.923256] pc : _raw_spin_unlock_irq+0x3c/0x78
[ 32.933817] x25: ffff0000081bb4a0
[ 32.937340] lr : _raw_spin_unlock_irq+0x38/0x78
[ 32.942465] sp : ffff00000ae73c60
[ 32.947455] x29: ffff00000ae73c60 x28: ffff00000978b000
[ 32.953060] x24: 0000000000000000
[ 32.967484] x23: 0000000000000000
[ 32.971265] x27: ffff8000d958db00
[ 32.976343] x22: 0000000000000000
[ 32.982508] x26: 0000000000000001
[ 32.996862] x21: ffff00000803bca4
[ 33.000630] x25: ffff8000d9e8a328
[ 33.005754] x20: ffff00000803bc80
[ 33.011888] x24: ffff000009087f88
[ 33.026057] x19: 0000000000000004
[ 33.029982] x23: ffff8000d971ad80
[ 33.035127] x18: 00000000000008bd
[ 33.041263] x22: ffff000009cbf000
[ 33.055312] x17: 00000000000008bc
[ 33.059310] x21: ffff8000d958db00
[ 33.064303] x16: ffff000009fd1360
[ 33.070605] x20: ffff0000080fc20c
[ 33.084645] x15: ffff000009f2a300
[ 33.088605] x19: ffff8000da7f4d40
[ 33.093572] x14: 00000000000017fc
[ 33.099943] x18: ffffffffffffffff
[ 33.114000] x13: 00000000c04846ac
[ 33.117948] x17: 0000000000000693
[ 33.122855] x12: ffff8000d9fc63b0
[ 33.129195] x16: ffff000009fcf7e0
[ 33.143370] x11: 0000000000000000
[ 33.147294] x15: ffff000009cbe1c8
[ 33.152152] x10: 0000000000000348
[ 33.158535] x14: 0000000000002fff
[ 33.172812] x9 : ffff8000d9590400
[ 33.176620] x13: 0000000016163b60
[ 33.181506] x8 : 000000000000001c
[ 33.187866] x12: ffff8000d971b630
[ 33.202251] x7 : ffff8000d9c08400
[ 33.205880] x11: 0000000000000000
[ 33.210939] x6 : 0000000000000364
[ 33.217236] x10: 0000000000000a48
[ 33.231721] x5 : 0000000000005356
[ 33.235281] x9 : ffff8000d9590c00
[ 33.240397] x4 : 0000000000000000
[ 33.246592] x8 : 000000000000001c
[ 33.261065] x3 : 0000000000000000
[ 33.264749] x7 : ffff8000d9c08400
[ 33.269874] x2 : ffff00000aabb000
[ 33.276019] x6 : 0000000000000a64
[ 33.290389] x1 : 0000000000000001
[ 33.294192] x5 : 000000000000cf1a
[ 33.299235] x0 : ffff8000d9fc5b00
[ 33.305452] x4 : 0000000000000000
[ 33.319989] Call trace:
[ 33.324715] x3 : 0000000000000000 x2 : ffff00000aabb000
[ 33.331717] multi_cpu_stop+0x100/0x168
[ 33.341973] x1 : 0000000000000001
[ 33.345891] cpu_stopper_thread+0xa8/0x118
[ 33.351777] smpboot_thread_fn+0x1bc/0x2c0
[ 33.357845] x0 : ffff8000d971ad80
[ 33.362176] kthread+0x134/0x138
[ 33.371281] Call trace:
[ 33.377420] ret_from_fork+0x10/0x1c
[ 33.382212] _raw_spin_unlock_irq+0x3c/0x78
[ 33.387685] finish_task_switch+0xa4/0x200
[ 33.396875] __schedule+0x350/0xc90
[ 33.408272] preempt_schedule_notrace+0x5c/0x130
[ 33.419484] ftrace_ops_no_ops+0xf4/0x180
[ 33.430795] ftrace_graph_call+0x0/0xc
[ 33.442095] preempt_count_add+0x1c/0x130
[ 33.453259] schedule+0x2c/0x98
[ 33.464586] worker_thread+0xdc/0x478
[ 33.475886] kthread+0x134/0x138
[ 33.487099] ret_from_fork+0x10/0x1c
[ 34.464807] rcu: INFO: rcu_preempt self-detected stall on CPU
[ 34.487238] rcu: 2-...0: (2757 ticks this GP) idle=20e/1/0x4000000000000002 softirq=120/120 fqs=316
5
[ 34.509364] rcu: (t=6514 jiffies g=-1095 q=1250)
[ 34.528505] Task dump for CPU 2:
[ 34.539317] migration/2 R running task 0 22 2 0x0000002a
[ 34.565716] Call trace:
[ 34.577387] dump_backtrace+0x0/0x200
[ 34.588782] show_stack+0x24/0x30
[ 34.600098] sched_show_task+0x20c/0x2d8
[ 34.611726] dump_cpu_task+0x48/0x58
[ 34.623109] rcu_dump_cpu_stacks+0xa0/0xe0
[ 34.634637] rcu_check_callbacks+0x85c/0xb60
[ 34.646324] update_process_times+0x34/0x60
[ 34.657569] tick_periodic+0x58/0x110
[ 34.669169] tick_handle_periodic+0x94/0xc8
[ 34.680719] arch_timer_handler_virt+0x38/0x58
[ 34.692090] handle_percpu_devid_irq+0xe4/0x458
[ 34.703783] generic_handle_irq+0x34/0x50
[ 34.715121] __handle_domain_irq+0x8c/0xf8
[ 34.726529] gic_handle_irq+0x84/0x180
[ 34.738131] el1_irq+0xec/0x198
[ 34.749285] multi_cpu_stop+0x100/0x168
[ 34.760840] cpu_stopper_thread+0xa8/0x118
[ 34.772384] smpboot_thread_fn+0x1bc/0x2c0
[ 34.783587] kthread+0x134/0x138
[ 34.795188] ret_from_fork+0x10/0x1c



Could perhaps
[ 32.821812] softirqs last enabled at (0): [<ffff0000080bdb68>] copy_process.isra.5.part.6+0x338/0x1ac
be involved in why the execution appears to never continue after the irq?


Kind regards,
Niklas

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