linux-kernel - Re: [patch 1/2] tick/broadcast: Prevent deep idle states if no broadcast device available

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Date:	Mon, 06 Jul 2015 18:57:57 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Sudeep Holla <sudeep.holla@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Suzuki Poulose <Suzuki.Poulose@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [patch 1/2] tick/broadcast: Prevent deep idle states if no broadcast
 device available



On 06/07/15 17:53, Thomas Gleixner wrote:
> On Mon, 6 Jul 2015, Sudeep Holla wrote:
>> On 06/07/15 17:06, Thomas Gleixner wrote:
>> 2. After boot I am seeing the below warning:
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 1 PID: 0 at kernel/time/hrtimer.c:1247
>> __hrtimer_run_queues+0x148/0x150()
>> Modules linked in:
>> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.2.0-rc1 #573
>> Hardware name: ARM Juno development board (r0) (DT)
>> Call trace:
>> [<ffffffc000089954>] dump_backtrace+0x0/0x124
>> [<ffffffc000089a88>] show_stack+0x10/0x1c
>> [<ffffffc0005d100c>] dump_stack+0x84/0xc8
>> [<ffffffc0000b3f34>] warn_slowpath_common+0x98/0xd0
>> [<ffffffc0000b402c>] warn_slowpath_null+0x14/0x20
>> [<ffffffc000101eec>] __hrtimer_run_queues+0x144/0x150
>> [<ffffffc0001028b4>] hrtimer_run_queues+0xb8/0xe8
>> [<ffffffc000101714>] update_process_times+0x28/0x6c
>> [<ffffffc00010d978>] tick_periodic+0x3c/0xb8
>> [<ffffffc00010da1c>] tick_handle_periodic+0x28/0x94
>> [<ffffffc0004d6154>] arch_timer_handler_phys+0x28/0x38
>> [<ffffffc0000f5964>] handle_percpu_devid_irq+0x74/0x9c
>> [<ffffffc0000f1668>] generic_handle_irq+0x30/0x4c
>> [<ffffffc0000f1984>] __handle_domain_irq+0x5c/0xac
>> [<ffffffc0000824a8>] gic_handle_irq+0x30/0x80
>
> Bah. I fear Preeti's hrtimer-broadcast stuff recurses in the hrtimer
> code.
>
> tick_periodic()
>    expire broadcast timer()
>      handle_broadcast() {
>        tick_periodic()
> 	 expire_other_timer()
>      }
>
>    warning triggers	
>
> Crap. Patch below should cure that.
>

This triggered the below crash on boot, looks like it's accessing
hrtimer->function which is null in periodic mode IIUC

Regards,
Sudeep

--->8

Bad mode in Synchronous Abort handler detected, code 0x86000005 -- IABT 
(current EL)
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.2.0-rc1 #577
Hardware name: ARM Juno development board (r0) (DT)
task: ffffffc976900000 ti: ffffffc9768fc000 task.ti: ffffffc9768fc000
PC is at 0x0
LR is at bc_handler+0x20/0x58
pc : [<0000000000000000>] lr : [<ffffffc00010f4a4>] pstate: a00001c5
sp : ffffffc9768ffbd0

Call trace:
[<          (null)>]           (null)
[<ffffffc000101e88>] __hrtimer_run_queues+0xe0/0x150
[<ffffffc0001028b4>] hrtimer_run_queues+0xb8/0xe8
[<ffffffc000101714>] update_process_times+0x28/0x6c
[<ffffffc00010d978>] tick_periodic+0x3c/0xb8
[<ffffffc00010da1c>] tick_handle_periodic+0x28/0x94
[<ffffffc0004d61d4>] arch_timer_handler_phys+0x28/0x38
[<ffffffc0000f5964>] handle_percpu_devid_irq+0x74/0x9c
[<ffffffc0000f1668>] generic_handle_irq+0x30/0x4c
[<ffffffc0000f1984>] __handle_domain_irq+0x5c/0xac
[<ffffffc0000824a8>] gic_handle_irq+0x30/0x80
--
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