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

[David Long <dave.long@linaro.org>]

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