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SubjectRe: [PATCH V1 1/1] tick: broadcast-hrtimer: Fix a race in bc_set_next
On Mon, Sep 23, 2019 at 09:51:54PM +0200, Thomas Gleixner wrote:
> On Wed, 18 Sep 2019, Balasubramani Vivekanandan wrote:
> >
> > When there are no more cpus subscribed to broadcast, the timer callback
> > might not set the expiry time for hrtimer. Therefore the callback timer
> > function is modified to set the state of broadcast clock to
> > CLOCK_EVT_STATE_ONESHOT_STOPPED which in turn will set the expiry time
> > of hrtimer to KTIME_MAX.
>
> That's an ugly layering violation, really.
>
> Aside of that the whole try to cancel logic and the comment that the
> hrtimer cannot be armed from within the callback is wrong. All of this can
> go way.
>
> Find a completely untested patch below [1]
>
> Thanks,
>
> tglx
>

jFTR, for the sake of anyone who lives on older kernels and happen to
deal with the same issue as reported by Balasubramani in this thread,
after enabling cpuidle [2-3] on R-Car H3ULCB (which seems to be a hard
prerequisite for seeing this issue reproduced), I got below [4,5,6]
backtraces on recent v5.3-12025-g4c07e2ddab5b using various intermittent
stress-ng loads. I believe they portray the issue reported by Bala.

I was not able to reproduce the RCU stalls after applying [1].

[1] https://lkml.org/lkml/2019/9/23/803
[2] https://patchwork.kernel.org/patch/10769701/
("[v2,1/5] arm64: dts: r8a7795: Add cpuidle support for CA57 cores")
[3] https://patchwork.kernel.org/patch/10769689/
("[v2,2/5] arm64: dts: r8a7795: Add cpuidle support for CA53 cores")

[4] RCU stall #1 reproduced on v5.3-12025-g4c07e2ddab5b + patches [2-3]

[ 701.628630] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[ 701.635259] rcu: 1-...!: (0 ticks this GP) idle=5b4/0/0x0 softirq=178953/178953 fqs=0 last_accelerate: c1a9/209c, Nonlazy posted: ..D
[ 701.648195] rcu: 3-...!: (667 GPs behind) idle=1a0/0/0x0 softirq=188640/188641 fqs=0 last_accelerate: c1a6/20a0, Nonlazy posted: .LD
[ 701.660666] rcu: 5-...!: (0 ticks this GP) idle=674/0/0x0 softirq=39323/39323 fqs=0 last_accelerate: c380/20a0, Nonlazy posted: ..D
[ 701.673046] rcu: 6-...!: (0 ticks this GP) idle=628/0/0x0 softirq=27147/27147 fqs=0 last_accelerate: c00c/20a0, Nonlazy posted: ..D
[ 701.685419] (detected by 2, t=25012 jiffies, g=392945, q=968)
[ 701.691487] Task dump for CPU 1:
[ 701.694873] swapper/1 R running task 0 0 1 0x00000028
[ 701.702227] Call trace:
[ 701.704822] __switch_to+0x2c4/0x2e8
[ 701.708578] num_spec.70129+0x177e7d/0x1d336c
[ 701.713130] Task dump for CPU 3:
[ 701.716514] swapper/3 R running task 0 0 1 0x00000028
[ 701.723865] Call trace:
[ 701.726445] __switch_to+0x2c4/0x2e8
[ 701.730192] 0x3
[ 701.732140] Task dump for CPU 5:
[ 701.735524] swapper/5 R running task 0 0 1 0x00000028
[ 701.742874] Call trace:
[ 701.745455] __switch_to+0x2c4/0x2e8
[ 701.749204] num_spec.70129+0x177e7d/0x1d336c
[ 701.753756] Task dump for CPU 6:
[ 701.757139] swapper/6 R running task 0 0 1 0x00000028
[ 701.764489] Call trace:
[ 701.767070] __switch_to+0x2c4/0x2e8
[ 701.770819] num_spec.70129+0x177e7d/0x1d336c
[ 701.775391] rcu: rcu_preempt kthread starved for 25068 jiffies! g392945 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=5
[ 701.786394] rcu: RCU grace-period kthread stack dump:
[ 701.791652] rcu_preempt I 0 10 2 0x00000028
[ 701.797369] Call trace:
[ 701.799944] __switch_to+0x2c4/0x2e8
[ 701.803688] __schedule+0xe1c/0xf58
[ 701.807337] schedule+0xc0/0x104
[ 701.810721] schedule_timeout+0x298/0x6ec
[ 701.814911] rcu_gp_kthread+0xf8c/0xf94
[ 701.818923] kthread+0x1c4/0x1dc
[ 701.822304] ret_from_fork+0x10/0x18
[ 701.826061] Kernel panic - not syncing: RCU Stall
[ 701.830964] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.3.0+ #18
[ 701.837201] Hardware name: Renesas H3ULCB Kingfisher board based on r8a7795 ES2.0+ (DT)
[ 701.845503] Call trace:
[ 701.848072] dump_backtrace+0x0/0x1ec
[ 701.851893] show_stack+0x24/0x30
[ 701.855361] dump_stack+0xcc/0x128
[ 701.858915] panic+0x288/0x5a4
[ 701.862112] panic_on_rcu_stall+0x2c/0x34
[ 701.866293] rcu_sched_clock_irq+0xe2c/0x1554
[ 701.870835] update_process_times+0x34/0x60
[ 701.875196] tick_sched_handle+0x80/0x98
[ 701.879286] tick_sched_timer+0x64/0xbc
[ 701.883289] __hrtimer_run_queues+0x5c8/0xb94
[ 701.887829] hrtimer_interrupt+0x1ec/0x454
[ 701.892107] arch_timer_handler_phys+0x40/0x58
[ 701.896737] handle_percpu_devid_irq+0x170/0x6f4
[ 701.901548] generic_handle_irq+0x3c/0x54
[ 701.905729] __handle_domain_irq+0x114/0x118
[ 701.910178] gic_handle_irq+0x70/0xac
[ 701.913999] el1_irq+0xbc/0x180
[ 701.917289] __asan_load8+0x40/0xb0
[ 701.920934] tick_check_broadcast_expired+0x70/0x8c
[ 701.926011] cpu_idle_poll+0x1ec/0x380
[ 701.929925] do_idle+0x188/0x354
[ 701.933301] cpu_startup_entry+0x28/0x2c
[ 701.937396] secondary_start_kernel+0x344/0x374
[ 701.942184] SMP: stopping secondary CPUs
[ 701.946316] Dumping ftrace buffer:
[ 701.950694] (ftrace buffer empty)
[ 701.954445] Kernel Offset: disabled
[ 701.958093] CPU features: 0x0002,21006004
[ 701.962274] Memory Limit: none
[ 701.965552] ---[ end Kernel panic - not syncing: RCU Stall ]---

[5] RCU stall #2 reproduced on v5.3-12025-g4c07e2ddab5b + patches [2-3]

[ 1193.212038] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:max-time=5 run; sleep 5; done
[ 1193.218757] rcu: 4-...!: (0 ticks this GP) idle=17c/0/0x0 softirq=130361/130361 fqs=1 last_accelerate: 9cdc/a0d9, Nonlazy posted: .LD
[ 1193.231958] (detected by 3, t=25021 jiffies, g=774405, q=58539)
[ 1193.238238] Task dump for CPU 4:
[ 1193.241641] swapper/4 R running task 0 0 1 0x00000028
[ 1193.249021] Call trace:
[ 1193.251631] __switch_to+0x2c4/0x2e8
[ 1193.255395] 0x1fffe000db4d0fe4
[ 1193.258720] rcu: rcu_preempt kthread starved for 7974 jiffies! g774405 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=4
[ 1193.270900] rcu: RCU grace-period kthread stack dump:
[ 1193.276542] rcu_preempt I 0 10 2 0x00000028
[ 1193.282278] Call trace:
[ 1193.284864] __switch_to+0x2c4/0x2e8
[ 1193.288619] __schedule+0xe1c/0xf58
[ 1193.292278] schedule+0xc0/0x104
[ 1193.295671] schedule_timeout+0x298/0x6ec
[ 1193.299875] rcu_gp_kthread+0xf8c/0xf94
[ 1193.303901] kthread+0x1c4/0x1dc
[ 1193.307295] ret_from_fork+0x10/0x18
[ 1193.311069] Kernel panic - not syncing: RCU Stall
[ 1193.315986] CPU: 3 PID: 2892 Comm: bash Not tainted 5.3.0+ #18
[ 1193.322056] Hardware name: Renesas H3ULCB Kingfisher board based on r8a7795 ES2.0+ (DT)
[ 1193.330372] Call trace:
[ 1193.332951] dump_backtrace+0x0/0x1ec
[ 1193.336782] show_stack+0x24/0x30
[ 1193.340259] dump_stack+0xcc/0x128
[ 1193.343822] panic+0x288/0x5a4
[ 1193.347026] panic_on_rcu_stall+0x2c/0x34
[ 1193.351217] rcu_sched_clock_irq+0xe2c/0x1554
[ 1193.355770] update_process_times+0x34/0x60
[ 1193.360141] tick_sched_handle+0x80/0x98
[ 1193.364240] tick_sched_timer+0x64/0xbc
[ 1193.368252] __hrtimer_run_queues+0x5c8/0xb94
[ 1193.372804] hrtimer_interrupt+0x1ec/0x454
[ 1193.377092] arch_timer_handler_phys+0x40/0x58
[ 1193.381734] handle_percpu_devid_irq+0x170/0x6f4
[ 1193.386558] generic_handle_irq+0x3c/0x54
[ 1193.390749] __handle_domain_irq+0x114/0x118
[ 1193.395208] gic_handle_irq+0x70/0xac
[ 1193.399037] el1_irq+0xbc/0x180
[ 1193.402333] lock_acquire+0x154/0x39c
[ 1193.406164] _raw_spin_lock+0x4c/0x88
[ 1193.409997] set_close_on_exec+0x44/0x1ac
[ 1193.414190] do_fcntl+0x578/0xbf4
[ 1193.417664] __arm64_sys_fcntl+0xa4/0xdc
[ 1193.421767] el0_svc_common.constprop.0+0x158/0x1f8
[ 1193.426854] el0_svc_handler+0x94/0xa0
[ 1193.430775] el0_svc+0x8/0xc
[ 1193.433878] SMP: stopping secondary CPUs
[ 1193.438059] Dumping ftrace buffer:
[ 1193.442613] (ftrace buffer empty)
[ 1193.446373] Kernel Offset: disabled
[ 1193.450028] CPU features: 0x0002,21006004
[ 1193.454217] Memory Limit: none
[ 1193.457508] ---[ end Kernel panic - not syncing: RCU Stall ]---

[6] RCU stall #3 reproduced on v5.3-12025-g4c07e2ddab5b + patches [2-3]

[66194.249069] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[66194.255718] rcu: 7-...!: (0 ticks this GP) idle=b34/0/0x0 softirq=1969905/1969905 fqs=1 last_accelerate: 36d8/7727, Nonlazy posted: .LD
[66194.268853] (detected by 2, t=25021 jiffies, g=8936349, q=98599)
[66194.275195] Task dump for CPU 7:
[66194.278585] swapper/7 R running task 0 0 1 0x00000028
[66194.285941] Call trace:
[66194.288537] __switch_to+0x2c4/0x2e8
[66194.292298] num_spec.70129+0x177e7d/0x1d336c
[66194.296872] rcu: rcu_preempt kthread starved for 16505 jiffies! g8936349 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=7
[66194.307968] rcu: RCU grace-period kthread stack dump:
[66194.313228] rcu_preempt I 0 10 2 0x00000028
[66194.318949] Call trace:
[66194.321527] __switch_to+0x2c4/0x2e8
[66194.325275] __schedule+0xe1c/0xf58
[66194.328926] schedule+0xc0/0x104
[66194.332310] schedule_timeout+0x298/0x6ec
[66194.336502] rcu_gp_kthread+0xf8c/0xf94
[66194.340516] kthread+0x1c4/0x1dc
[66194.343900] ret_from_fork+0x10/0x18
[66194.347664] Kernel panic - not syncing: RCU Stall
[66194.352574] CPU: 2 PID: 17232 Comm: stress-ng-cpu Not tainted 5.3.0+ #18
[66194.359535] Hardware name: Renesas H3ULCB Kingfisher board based on r8a7795 ES2.0+ (DT)
[66194.367848] Call trace:
[66194.370428] dump_backtrace+0x0/0x1ec
[66194.374256] show_stack+0x24/0x30
[66194.377730] dump_stack+0xcc/0x128
[66194.381288] panic+0x288/0x5a4
[66194.384493] panic_on_rcu_stall+0x2c/0x34
[66194.388680] rcu_sched_clock_irq+0xe2c/0x1554
[66194.393229] update_process_times+0x34/0x60
[66194.397595] tick_sched_handle+0x80/0x98
[66194.401691] tick_sched_timer+0x64/0xbc
[66194.405700] __hrtimer_run_queues+0x5c8/0xb94
[66194.410246] hrtimer_interrupt+0x1ec/0x454
[66194.414528] arch_timer_handler_phys+0x40/0x58
[66194.419167] handle_percpu_devid_irq+0x170/0x6f4
[66194.423990] generic_handle_irq+0x3c/0x54
[66194.428178] __handle_domain_irq+0x114/0x118
[66194.432630] gic_handle_irq+0x70/0xac
[66194.436454] el0_irq_naked+0x50/0x5c
[66194.440261] SMP: stopping secondary CPUs
[66194.444571] Dumping ftrace buffer:
[66194.449132] (ftrace buffer empty)
[66194.452890] Kernel Offset: disabled
[66194.456538] CPU features: 0x0002,21006004
[66194.460719] Memory Limit: none
[66194.463997] ---[ end Kernel panic - not syncing: RCU Stall ]---

--
Best Regards,
Eugeniu

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