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

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Message-ID: <20141209133340.GA20265@linaro.org>
Date:	Tue, 9 Dec 2014 13:33:42 +0000
From:	Steve Capper <steve.capper@...aro.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	David Long <dave.long@...aro.org>,
	"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 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.

Cheers,
-- 
Steve
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