On Wed, Dec 16, 2020 at 05:29:39PM +0000, Qais Yousef wrote:
> Hi Paul
>
> We hit the below splat a couple of days ago in our testing. Sadly I can't
> reproduce it. And it was on android-mainline branch..
>
> It's the deadlock message that bothers me. I can't see how we could have ended
> there. We detect a stall and when trying to dump the stack LOCKDEP spits the
> warning.
>
> Maybe should take this report with a pinch of salt since it wasn't on
> mainline.
> I just thought it might be something worth sharing in case you can actually
> spot something obvious that I can't see. If I got more info or a reproducer
> I will share them.
>
> The failure was triggered twice on that day running 2 different tests.
This looks like the same problem that Mark Rutland's recent patch series
was fixing. Do you have this series applied?
lore.kernel.org/lkml/20201126123602.23454-1-mark.rutl...@arm.com
Thanx, Paul
> [ 310.073379] LTP: starting leapsec01
> [ 345.070123] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 345.076717] rcu: 0-...!: (1 ticks this GP) idle=798/0/0x0
> softirq=19187/19187 fqs=0 (false positive?)
> [ 345.087533] (detected by 2, t=6502 jiffies, g=57249, q=184)
> [ 345.093284]
> [ 345.094797] ============================================
> [ 345.100139] WARNING: possible recursive locking detected
> [ 345.105485] 5.10.0-rc7-02296-g3f43bd6f2c3b-ab89 #1 Not tainted
> [ 345.111349] --------------------------------------------
> [ 345.116693] swapper/2/0 is trying to acquire lock:
> [ 345.121515] ffffa00013b50c58 (rcu_node_0){-.-.}-{2:2}, at:
> rcu_dump_cpu_stacks+0x7c/0x14c
> [ 345.129813]
> [ 345.129813] but task is already holding lock:
> [ 345.135678] ffffa00013b50c58 (rcu_node_0){-.-.}-{2:2}, at:
> rcu_sched_clock_irq+0x68c/0x11c0
> [ 345.144143]
> [ 345.144143] other info that might help us debug this:
> [ 345.150702] Possible unsafe locking scenario:
> [ 345.150702]
> [ 345.156651] CPU0
> [ 345.159119] ----
> [ 345.161585] lock(rcu_node_0);
> [ 345.164779] lock(rcu_node_0);
> [ 345.167973]
> [ 345.167973] *** DEADLOCK ***
> [ 345.167973]
> [ 345.173923] May be due to missing lock nesting notation
> [ 345.173923]
> [ 345.180746] 1 lock held by swapper/2/0:
> [ 345.184607] #0: ffffa00013b50c58 (rcu_node_0){-.-.}-{2:2}, at:
> rcu_sched_clock_irq+0x68c/0x11c0
> [ 345.193517]
> [ 345.193517] stack backtrace:
> [ 345.197910] CPU: 2 PID: 0 Comm: swapper/2 Not tainted
> 5.10.0-rc7-02296-g3f43bd6f2c3b-ab89 #1
> [ 345.206389] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno
> Development Platform, BIOS EDK II Oct 19 2019
> [ 345.217215] Call trace:
> [ 345.219691] dump_backtrace+0x0/0x2b8
> [ 345.223383] show_stack+0x18/0x68
> [ 345.226731] dump_stack+0x110/0x188
> [ 345.230255] __lock_acquire+0x23f0/0x2410
> [ 345.234300] lock_acquire+0x3b8/0x730
> [ 345.237997] _raw_spin_lock_irqsave+0x80/0x168
> [ 345.242476] rcu_dump_cpu_stacks+0x7c/0x14c
> [ 345.246693] rcu_sched_clock_irq+0xfd4/0x11c0
> [ 345.251087] update_process_times+0x84/0xe0
> [ 345.255306] tick_sched_handle.isra.0+0x68/0x98
> [ 345.259871] tick_sched_timer+0x60/0xd8
> [ 345.263742] __hrtimer_run_queues+0x534/0x9e0
> [ 345.268134] hrtimer_interrupt+0x1a8/0x398
> [ 345.272264] tick_receive_broadcast+0x60/0x88
> [ 345.276657] ipi_handler+0x250/0x4b8
> [ 345.280270] handle_percpu_devid_fasteoi_ipi+0x138/0x4f0
> [ 345.285619] generic_handle_irq+0x4c/0x68
> [ 345.289661] __handle_domain_irq+0x9c/0x118
> [ 345.293880] gic_handle_irq+0xdc/0x118
> [ 345.297661] el1_irq+0xc8/0x180
> [ 345.300835] cpuidle_enter_state+0x16c/0x810
> [ 345.305139] cpuidle_enter+0x4c/0x78
> [ 345.308749] call_cpuidle+0x44/0x88
> [ 345.312271] do_idle+0x2d4/0x338
> [ 345.315532] cpu_startup_entry+0x24/0x68
> [ 345.319491] secondary_start_kernel+0x1d4/0x2d8
>
> Thanks
>
> --
> Qais Yousef
