Hi
On 07/21/21 13:21, Paul E. McKenney wrote:
> From: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
>
> If rcu_print_task_stall() is invoked on an rcu_node structure that does
> not contain any tasks blocking the current grace period, it takes an
> early exit that fails to release that rcu_node structure's lock. This
> results in a self-deadlock, which is detected by lockdep.
>
> To reproduce this bug:
>
> tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 3 --trust-make --configs "TREE03" --kconfig "CONFIG_PROVE_LOCKING=y" --bootargs "rcutorture.stall_cpu=30 rcutorture.stall_cpu_block=1 rcutorture.fwd_progress=0 rcutorture.test_boost=0"
>
> This will also result in other complaints, including RCU's scheduler
> hook complaining about blocking rather than preemption and an rcutorture
> writer stall.
>
> Only a partial RCU CPU stall warning message will be printed because of
> the self-deadlock.
>
> This commit therefore releases the lock on the rcu_print_task_stall()
> function's early exit path.
>
> Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled")
> Signed-off-by: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
We are seeing similar stall/deadlock issue on android 5.10 kernel, is the fix
relevant here? Trying to apply the patches and test, but the problem is tricky
to reproduce so thought worth asking first.
[ 1010.244334] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:"}
[ 1010.250538] rcu: \t2-...!: (42 GPs behind) idle=884/0/0x0 softirq=1646/1647 fqs=0 (false positive?)"}
[ 1010.259746] rcu: \t3-...!: (1 ticks this GP) idle=134/0/0x0 softirq=3205/3205 fqs=0 (false positive?)"}
[ 1010.269013] \t(detected by 4, t=6502 jiffies, g=9121, q=110)"}
[ 1010.274621] "}
[ 1010.276115] ============================================"}
[ 1010.281438] WARNING: possible recursive locking detected"}
[ 1010.286763] 5.10.43-g92fdbb553f50-ab979 #1 Not tainted"}
[ 1010.291912] --------------------------------------------"}
[ 1010.297235] swapper/4/0 is trying to acquire lock:"}
[ 1010.302037] ffff8000121fe618 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0x60/0xf8"}
[ 1010.310183] "}
[ 1010.310183] but task is already holding lock:"}
[ 1010.316028] ffff8000121fe618 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq+0x658/0xca0"}
[ 1010.324341] "}
[ 1010.324341] other info that might help us debug this:"}
[ 1010.330882] Possible unsafe locking scenario:"}
[ 1010.330882] "}
[ 1010.336813] CPU0"}
[ 1010.339263] ----"}
[ 1010.341713] lock(rcu_node_0);"}
[ 1010.344872] lock(rcu_node_0);"}
[ 1010.348029] "}
[ 1010.348029] *** DEADLOCK ***"}
[ 1010.348029] "}
[ 1010.353961] May be due to missing lock nesting notation"}
[ 1010.353961] "}
[ 1010.360764] 1 lock held by swapper/4/0:"}
[ 1010.364607] #0: ffff8000121fe618 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq+0x658/0xca0"}
[ 1010.373359] "}
[ 1010.373359] stack backtrace:"}
[ 1010.377729] CPU: 4 PID: 0 Comm: swapper/4 Not tainted 5.10.43-g92fdbb553f50-ab979 #1"}
[ 1010.385489] Hardware name: ARM Juno development board (r0) (DT)"}
[ 1010.391421] Call trace:"}
[ 1010.393877] dump_backtrace+0x0/0x1c0"}
[ 1010.397551] show_stack+0x24/0x30"}
[ 1010.400877] dump_stack_lvl+0xf4/0x130"}
[ 1010.404636] dump_stack+0x18/0x58"}
[ 1010.407962] __lock_acquire+0xa18/0x1ffc"}
[ 1010.411895] lock_acquire.part.0+0xc8/0x30c"}
[ 1010.416089] lock_acquire+0x68/0x84"}
[ 1010.419589] _raw_spin_lock_irqsave+0x84/0x158"}
[ 1010.424045] rcu_dump_cpu_stacks+0x60/0xf8"}
[ 1010.428154] rcu_sched_clock_irq+0x8d8/0xca0"}
[ 1010.432435] update_process_times+0x6c/0xb0"}
[ 1010.436632] tick_sched_handle+0x3c/0x60"}
[ 1010.440566] tick_sched_timer+0x58/0xb0"}
[ 1010.444412] __hrtimer_run_queues+0x1a4/0x5b0"}
[ 1010.448781] hrtimer_interrupt+0xf4/0x2cc"}
[ 1010.452803] arch_timer_handler_phys+0x40/0x50"}
[ 1010.457260] handle_percpu_devid_irq+0x98/0x180"}
[ 1010.461803] __handle_domain_irq+0x80/0xec"}
[ 1010.465911] gic_handle_irq+0x5c/0xf0"}
[ 1010.469583] el1_irq+0xcc/0x180"}
[ 1010.472735] cpuidle_enter_state+0xe8/0x350"}
[ 1010.476929] cpuidle_enter+0x44/0x60"}
[ 1010.480515] do_idle+0x25c/0x2f0"}
[ 1010.483751] cpu_startup_entry+0x34/0x8c"}
[ 1010.487687] secondary_start_kernel+0x154/0x190"}
Thanks
--
Qais Yousef
