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Date: Wed, 16 Dec 2020 17:29:39 +0000
From: Qais Yousef <qais.yousef@....com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
linux-kernel@...r.kernel.org
Subject: RCU stall leading to deadlock warning
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.
[ 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
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