linux-kernel - Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...'

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <56C22105.6050900@arm.com>
Date:	Mon, 15 Feb 2016 19:03:33 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-next@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace
 timers with utilization ...'

On 15/02/16 18:54, Rafael J. Wysocki wrote:
> On Mon, Feb 15, 2016 at 7:49 PM, Marc Zyngier <marc.zyngier@....com> wrote:
>> On 15/02/16 18:41, Rafael J. Wysocki wrote:
>>> On Mon, Feb 15, 2016 at 6:05 PM, Guenter Roeck <linux@...ck-us.net> wrote:
>>>> Rafael,
>>>
>>> Hi,
>>>
>>> Thanks for the report!
>>>
>>>> I see crashes in various arm qemu tests due to 'cpufreq: governor: Replace
>>>> timers with utilization update callbacks' with next-20160215. An example
>>>> crash log and bisect results are attached below.
>>>>
>>>> Please let me know if there is anything I can do to help tracking down
>>>> the problem.
>>>
>>> It looks like we've uncovered some nastiness in the arch ARM code (see below).
>>>
>>> [cut]
>>>
>>>> [    1.340000] Unable to handle kernel NULL pointer dereference at virtual address 00000000
>>>> [    1.340000] pgd = c0204000
>>>> [    1.340000] [00000000] *pgd=00000000
>>>> [    1.340000] Internal error: Oops: 80000005 [#1] SMP ARM
>>>> [    1.340000] Modules linked in:
>>>> [    1.340000] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.5.0-rc4-next-20160215 #1
>>>> [    1.340000] Hardware name: Generic OMAP3-GP (Flattened Device Tree)
>>>> [    1.340000] task: cb060000 ti: cb05a000 task.ti: cb05a000
>>>> [    1.340000] PC is at 0x0
>>>> [    1.340000] LR is at arch_send_call_function_single_ipi+0x34/0x38
>>>
>>> Since this is ARM, arch_send_call_function_single_ipi() looks like this:
>>>
>>> void arch_send_call_function_single_ipi(int cpu)
>>> {
>>>          smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE);
>>> }
>>>
>>> so I'm not sure how the NULL pointer deref is possible even.
>>>
>>> The only thing coming to mind would be that cpumask_of(cpu) triggers
>>> this, but I'm not sure how exactly that can happen.
>>>
>>> I need help from somebody who knows how this low-level stuff works on ARM.
>>
>> Given that OMAP3 is a UP system, there is zero chance that it has
>> registered the magic hook that delivers IPIs (its interrupt controller
>> is not even capable of doing so).
>>
>> I don't really know the context, but IPIs on a UP system seem at best odd.
> 
> That would explain it, thanks.
> 
> So it looks like we should always use irq_work_queue() on UP even if
> CONFIG_SMP is set, shouldn't we?

Something like that, yes. CONFIG_SMP is not an indication of an SMP
system anymore (we've even dropped the config option on arm64).

Hopefully num_possible_cpus() is reliable enough to let you do the right
thing...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...