Date:   Tue, 30 Aug 2016 16:22:30 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Pratyush Anand <panand@...hat.com>
Cc:     mingo@...nel.org, alexandre.belloni@...e-electrons.com,
        tglx@...utronix.de, hpa@...or.com, x86@...nel.org,
        rtc-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        prarit@...hat.com, dzickus@...hat.com, a.zummo@...ertech.it
Subject: Re: [PATCH V3 2/2] rtc/rtc-cmos: Initialize software counters before
 irq is registered

Hi, Pratyush

On 08/16/16 at 08:55am, Pratyush Anand wrote:
> We have observed on few x86 machines with rtc-cmos device that
> hpet_rtc_interrupt() is called just after irq registration and before
> cmos_do_probe() could call hpet_rtc_timer_init().
> 
> So, neither hpet_default_delta nor hpet_t1_cmp is initialized by the time
> interrupt is raised in the given situation, and this results in NMI
> watchdog LOCKUP.
> 
> It has only been observed sporadically on kdump secondary kernels.
> 
> See the call trace:
> ---<-snip->---
>    27.913194] Kernel panic - not syncing: Watchdog detected hard LOCKUP on
> cpu 0
> [   27.915371] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
> 3.10.0-342.el7.x86_64 #1
> [   27.917503] Hardware name: HP ProLiant DL160 Gen8, BIOS J03 02/10/2014
> [   27.919455]  ffffffff8186a728 0000000059c82488 ffff880034e05af0
> ffffffff81637bd4
> [   27.921870]  ffff880034e05b70 ffffffff8163144a 0000000000000010
> ffff880034e05b80
> [   27.924257]  ffff880034e05b20 0000000059c82488 0000000000000000
> 0000000000000000
> [   27.926599] Call Trace:
> [   27.927352]  <NMI>  [<ffffffff81637bd4>] dump_stack+0x19/0x1b
> [   27.929080]  [<ffffffff8163144a>] panic+0xd8/0x1e7
> [   27.930588]  [<ffffffff8111d3e0>] ? restart_watchdog_hrtimer+0x50/0x50
> [   27.932502]  [<ffffffff8111d4a2>] watchdog_overflow_callback+0xc2/0xd0
> [   27.934427]  [<ffffffff811612c1>] __perf_event_overflow+0xa1/0x250
> [   27.936232]  [<ffffffff81161d94>] perf_event_overflow+0x14/0x20
> [   27.937957]  [<ffffffff81032ae8>] intel_pmu_handle_irq+0x1e8/0x470
> [   27.939799]  [<ffffffff8164164b>] perf_event_nmi_handler+0x2b/0x50
> [   27.941649]  [<ffffffff81640d99>] nmi_handle.isra.0+0x69/0xb0
> [   27.943348]  [<ffffffff81640f49>] do_nmi+0x169/0x340
> [   27.944802]  [<ffffffff816401d3>] end_repeat_nmi+0x1e/0x2e
> [   27.946424]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
> [   27.948197]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
> [   27.949992]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
> [   27.951816]  <<EOE>>  <IRQ>  [<ffffffff8108f5a3>] ?
> run_timer_softirq+0x43/0x340
> [   27.954114]  [<ffffffff8111e24e>] handle_irq_event_percpu+0x3e/0x1e0
> [   27.955962]  [<ffffffff8111e42d>] handle_irq_event+0x3d/0x60
> [   27.957635]  [<ffffffff811210c7>] handle_edge_irq+0x77/0x130
> [   27.959332]  [<ffffffff8101704f>] handle_irq+0xbf/0x150
> [   27.960949]  [<ffffffff8164a86f>] do_IRQ+0x4f/0xf0
> [   27.962434]  [<ffffffff8163faed>] common_interrupt+0x6d/0x6d
> [   27.964101]  <EOI>  [<ffffffff8163f43b>] ?
> _raw_spin_unlock_irqrestore+0x1b/0x40
> [   27.966308]  [<fffff8111ff07>] __setup_irq+0x2a7/0x570
> [   28.067859]  [<ffffffff81056e60>] ? hpet_cpuhp_notify+0x140/0x140
> [   28.069709]  [<ffffffff8112032c>] request_threaded_irq+0xcc/0x170
> [   28.071585]  [<ffffffff814b24a6>] cmos_do_probe+0x1e6/0x450
> [   28.073240]  [<ffffffff814b2710>] ? cmos_do_probe+0x450/0x450
> [   28.074911]  [<ffffffff814b27cb>] cmos_pnp_probe+0xbb/0xc0
> [   28.076533]  [<ffffffff8139b245>] pnp_device_probe+0x65/0xd0
> [   28.078198]  [<ffffffff813f8ca7>] driver_probe_device+0x87/0x390
> [   28.079971]  [<ffffffff813f9083>] __driver_attach+0x93/0xa0
> [   28.081660]  [<ffffffff813f8ff0>] ? __device_attach+0x40/0x40
> [   28.083662]  [<ffffffff813f6a13>] bus_for_each_dev+0x73/0xc0
> [   28.085370]  [<ffffffff813f86fe>] driver_attach+0x1e/0x20
> [   28.086974]  [<ffffffff813f8250>] bus_add_driver+0x200/0x2d0
> [   28.088634]  [<ffffffff81ade49a>] ? rtc_sysfs_init+0xe/0xe
> [   28.090349]  [<ffffffff813f9704>] driver_register+0x64/0xf0
> [   28.091989]  [<ffffffff8139b070>] pnp_register_driver+0x20/0x30
> [   28.093707]  [<ffffffff81ade4ab>] cmos_init+0x11/0x71
> ---<-snip->---
> 
> The previous patch split hpet_rtc_timer_init into
> hpet_rtc_timer_counter_init() and hpet_rtc_timer_enable().
> 
> Therefore, this patch moved hpet_rtc_timer_counter_init() before IRQ
> registration, so that we can gracefully handle such spurious interrupts.
> 
> We were able to reproduce the problem in maximum 15 trials of kdump
> secondary kernel boot on an hp-dl160gen8 machine without this patch.
> However, more than 35 trials went fine after applying this patch.
> 
> Signed-off-by: Pratyush Anand <panand@...hat.com>
> [dzickus@...hat.com: edited the patch's summary]
> Signed-off-by: Don Zickus <dzickus@...hat.com>
> ---
>  drivers/rtc/rtc-cmos.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> index 43745cac0141..089d987f2638 100644
> --- a/drivers/rtc/rtc-cmos.c
> +++ b/drivers/rtc/rtc-cmos.c
> @@ -129,6 +129,16 @@ static inline int hpet_rtc_dropped_irq(void)
>  	return 0;
>  }
>  
> +static inline int hpet_rtc_timer_counter_init(void)
> +{
> +	return 0;
> +}
> +
> +static inline int hpet_rtc_timer_enable(void)
> +{
> +	return 0;
> +}
> +

Can these dummy functions go to /usr/include/linux/hpet.h alont with
the #ifdef  etc.

>  static inline int hpet_rtc_timer_init(void)
>  {
>  	return 0;
> @@ -707,6 +717,7 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
>  		goto cleanup1;
>  	}
>  
> +	hpet_rtc_timer_counter_init();
>  	if (is_valid_irq(rtc_irq)) {
>  		irq_handler_t rtc_cmos_int_handler;
>  
> @@ -729,7 +740,7 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
>  			goto cleanup1;
>  		}
>  	}
> -	hpet_rtc_timer_init();
> +	hpet_rtc_timer_enable();
>  
>  	/* export at least the first block of NVRAM */
>  	nvram.size = address_space - NVRAM_OFFSET;
> -- 
> 2.5.5
> 

Thanks
Dave

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