Messages in this thread | | | Date | Wed, 26 Nov 2014 12:46:53 -0500 | From | David Long <> | Subject | Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support |
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On 11/26/14 05:03, 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. > > I rebooted, set up the kprobe, then ran `./hackbench 100 process 1000', > to try and exacerbate things, and got the following: > # cat /sys/kernel/debug/tracing/kprobe_profile > memcpy 100677 0 > > So no missed events thusfar. > > Cheers, >
So I take it from this we can conclude the problem is not reliably reproducible?
-dl
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