linux-kernel - Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support

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Date:	Tue, 09 Dec 2014 09:27:18 -0500
From:	David Long <dave.long@...aro.org>
To:	Steve Capper <steve.capper@...aro.org>
CC:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	William Cohen <wcohen@...hat.com>,
	David Miller <davem@...emloft.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support

On 12/09/14 08:33, Steve Capper wrote:
> On Thu, Dec 04, 2014 at 08:53:03PM +0900, Masami Hiramatsu wrote:
>> (2014/12/04 20:29), Steve Capper wrote:
>>
>>>> I'd like to ask you to try my fix on your machine, with my reproducing
>>>> methods. (do not use sytemtap nor perf, those can have other issues)
>>>>
>>>
>>> Thank you Masami,
>>>
>>> I tried the following commands:
>>>
>>> echo "p:trace_event_buffer_lock_reserve
>>> trace_event_buffer_lock_reserve" >
>>> /sys/kernel/debug/tracing/kprobe_events
>>> echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
>>> echo 1 > /sys/kernel/debug/tracing/events/sched/sched_process_exec/enable
>>>
>>> The system appeared okay, I then cat'ed out:
>>> # cat /sys/kernel/debug/tracing/kprobe_profile
>>>     trace_event_buffer_lock_reserve                           25              25
>>>
>>> I got similar output (i.e. no crashes) both with and without the
>>> interrupt fix you recommended.
>>>
>>> I'm not sure how to interpret this, please let me know if you would
>>> like me to run any other tests?
>>>
>>> (I did also try your proposed fix with perf + memcpy and that crashed
>>> in a similar way as before).
>>
>> Hmm, then the bug is still there, and the bug may not be in the recursive
>> call path... We need to find another suspicious code in the patch.
>>
>
> Not sure if this is helpful, but the following also caused a crash for
> me:
>
> echo "p:trace_event_buffer_lock_reserve trace_event_buffer_lock_reserve" > /sys/kernel/debug/tracing/kprobe_events
> echo "p:memcpy memcpy" >> /sys/kernel/debug/tracing/kprobe_events
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
>
> [immediate crash]
>
> The crash point for me is in the arm64 ASID allocator, it again looks
> like the interrupts are in an unexpected state.
> (check_and_switch_context goes down the irqs disabled code path, I
> think incorrectly).
>
> This occurred for me both with and without the proposed irq saving fix.
>
> I will do some more digging.
>

Thanks, more information is good.

-dl


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