From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
To: Steve Capper <steve.capper@linaro.org>
Cc: David Long <dave.long@linaro.org>,
linux-arm-kernel@lists.infradead.org,
Russell King <linux@arm.linux.org.uk>,
"Jon Medhurst (Tixy)" <tixy@linaro.org>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Sandeepa Prabhu <sandeepa.prabhu@linaro.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
William Cohen <wcohen@redhat.com>,
davem@davemloft.net
Subject: Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support
Date: Thu, 27 Nov 2014 14:13:05 +0900 [thread overview]
Message-ID: <5476B2E1.7030304@hitachi.com> (raw)
In-Reply-To: <20141126100325.GA9157@linaro.org>
(2014/11/26 19:03), Steve Capper wrote:
> On Wed, Nov 26, 2014 at 05:33:05PM +0900, Masami Hiramatsu wrote:
>> (2014/11/21 0:02), Steve Capper wrote:
>>> On Tue, Nov 18, 2014 at 01:32:50AM -0500, David Long wrote:
>>>> From: "David A. Long" <dave.long@linaro.org>
>>>>
>>>> This patchset is heavily based on Sandeepa Prabhu's ARM v8 kprobes patches, first
>>>> seen in October 2013. This version attempts to address concerns raised by
>>>> reviewers and also fixes problems discovered during testing, particularly during
>>>> SMP testing.
>>>>
>>>> This patchset adds support for kernel probes(kprobes), jump probes(jprobes)
>>>> and return probes(kretprobes) support for ARM64.
>>>>
>>>> Kprobes mechanism makes use of software breakpoint and single stepping
>>>> support available in the ARM v8 kernel.
>>>>
>>>> Changes since v2 include:
>>>>
>>>> 1) Removal of NOP padding in kprobe XOL slots. Slots are now exactly one
>>>> instruction long.
>>>> 2) Disabling of interrupts during execution in single-step mode.
>>>> 3) Fixing of numerous problems in instruction simulation code.
>>>> 4) Support for the HAVE_REGS_AND_STACK_ACCESS_API feature is added, to allow
>>>> access to kprobes through debugfs.
>>>> 5) kprobes is *not* enabled in defconfig.
>>>> 6) Numerous complaints from checkpatch have been cleaned up, although a couple
>>>> remain as removing the function pointer typedefs results in ugly code.
>>>
>>> Hi David,
>>> I've been playing with this on a Juno board.
>>> I ran into one crash, which I'm not yet sure is an issue, but thought I
>>> would flag it.
>>>
>>> I opted to put a kprobe on memcpy, this is an assembler function so I
>>> located it via:
>>> $ nm ./vmlinux | grep \ memcpy$
>>> fffffe0000408a00 T memcpy
>>>
>>> Then placed a probe as follows:
>>> echo "p:memcpy 0xfffffe0000408a00 %x2" > /sys/kernel/debug/tracing/kprobe_events
>>
>> You can also do "p:memcpy memcpy %x2" > ...
>
> Thanks, that is easier :-).
>
>>
>>>
>>> I was able to cat out the /sys/kernel/debug/tracing/trace_pipe file and
>>> activate the probe via:
>>> echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
>>>
>>> Everything worked well, and I got the expected output.
>>>
>>> I then tried to record events with perf via:
>>> perf record -e kprobes:memcpy -a sleep 5
>>>
>>> Then I got an, easily reproducible, panic (pasted below).
>>
>> On x86, I didn't get a panic.
>>
>>>
>>> The point of failure in the panic was:
>>> fs/buffer.c:1257
>>>
>>> static inline void check_irqs_on(void)
>>> {
>>> #ifdef irqs_disabled
>>> BUG_ON(irqs_disabled());
>>> #endif
>>> }
>>>
>>> I will do some more digging; but I have managed to code up an ftrace
>>> static probe on memcpy and record that using perf on arm64 without
>>> issue.
>>
>> Yeah, this can be a bug related to kprobes recursive call.
>> Could you do "cat /sys/kernel/debug/tracing/kprobe_profile" (before
>> run perf)?
>> The first digit is # of hit, and the second is # of missed (since
>> recursively called).
>>
>> On x86, right after tracing by ftrace, we have no missed probe.
>>
>> # cat /sys/kernel/debug/tracing/kprobe_profile
>> memcpy 4547 0
>>
>> But after tracing by perf, many missed events I could see.
>>
>> # cat /sys/kernel/debug/tracing/kprobe_profile
>> memcpy 413983 7632
>>
>> So I guess this can be related to the recursive call (which
>> is correctly handled on x86).
>>
>
> Before running perf, I got the following:
>
> # cat /sys/kernel/debug/tracing/kprobe_profile
> memcpy 838 0
>
> Unfortunately, after the crash, I was then unable to take any other
> measurements.
Yes, but we can ensure that the recursion must be occur by
probing kprobe-tracer (ftrace) itself.
E.g.
Ensure trace_event_buffer_lock_reserve exists.
# grep trace_event_buffer_lock_reserve /proc/kallsyms
ffffffff8113a100 T trace_event_buffer_lock_reserve
Define a probe on it.
# echo p:test trace_event_buffer_lock_reserve > kprobe_events
And enable with another event (because this probe is not hit unless
other events hit)
# echo 1 > events/kprobes/test/enable
# echo 1 > events/sched/sched_process_exec/enable
If recursive call has a problem, you'll have a panic if you execute
any command. Anyway, on x86, we can see below result.
# cat kprobe_profile
test 1 1
So, the half of all probes will be missed.
Thank you,
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com
prev parent reply other threads:[~2014-11-27 5:13 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-18 6:32 [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support David Long
2014-11-18 6:32 ` [PATCH v3 1/5] arm64: Kprobes with single stepping support David Long
2014-11-18 13:28 ` Jon Medhurst (Tixy)
2014-11-21 4:28 ` David Long
2014-11-18 14:38 ` William Cohen
2014-11-18 14:39 ` William Cohen
2014-11-18 14:56 ` Will Deacon
2014-11-19 11:21 ` Sandeepa Prabhu
2014-11-19 11:25 ` Will Deacon
2014-11-19 14:55 ` David Long
2014-11-20 5:10 ` Sandeepa Prabhu
2014-11-26 6:46 ` David Long
2014-11-26 10:09 ` Will Deacon
2014-12-22 10:10 ` Pratyush Anand
2014-11-18 6:32 ` [PATCH v3 2/5] arm64: Kprobes instruction simulation support David Long
2014-11-18 14:43 ` William Cohen
2014-11-18 6:32 ` [PATCH v3 3/5] arm64: Add kernel return probes support(kretprobes) David Long
2014-11-18 14:50 ` William Cohen
2014-11-18 6:32 ` [PATCH v3 4/5] kprobes: Add arm64 case in kprobe example module David Long
2014-11-18 6:32 ` [PATCH v3 5/5] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature David Long
2014-11-18 14:52 ` Will Deacon
2014-11-20 7:20 ` Masami Hiramatsu
2014-11-21 6:16 ` David Long
2014-11-20 15:02 ` [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support Steve Capper
2014-11-26 8:33 ` Masami Hiramatsu
2014-11-26 10:03 ` Steve Capper
2014-11-26 17:46 ` David Long
2014-11-26 18:59 ` Steve Capper
2014-11-27 6:07 ` Masami Hiramatsu
2014-11-28 16:01 ` Steve Capper
2014-12-01 9:37 ` Masami Hiramatsu
2014-12-02 19:27 ` William Cohen
2014-12-02 20:00 ` William Cohen
2014-12-03 3:36 ` Masami Hiramatsu
2014-12-03 14:54 ` William Cohen
2014-12-03 22:54 ` David Long
2014-12-04 0:02 ` David Long
2014-12-04 1:16 ` William Cohen
2014-12-04 2:48 ` David Long
2014-12-04 10:21 ` Steve Capper
2014-12-04 10:43 ` Masami Hiramatsu
2014-12-04 11:29 ` Steve Capper
2014-12-04 11:53 ` Masami Hiramatsu
2014-12-09 13:33 ` Steve Capper
2014-12-09 14:27 ` David Long
2014-12-10 16:38 ` Steve Capper
2014-12-12 22:42 ` David Long
2014-12-12 23:10 ` Steve Capper
2014-12-15 5:58 ` Masami Hiramatsu
2014-12-15 6:29 ` David Long
2014-12-05 5:08 ` William Cohen
2014-11-27 5:13 ` Masami Hiramatsu [this message]
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