[BUG?]3.0-rc4+ftrace+kprobe: set kprobe at instruction 'stwu' lead to system crash/freeze

[Yong Zhang]

On Mon, Jun 27, 2011 at 6:01 PM, Ananth N Mavinakayanahalli
<ananth at in.ibm.com> wrote:
> On Sun, Jun 26, 2011 at 11:47:13PM +0900, Masami Hiramatsu wrote:
>> (2011/06/24 19:29), Steven Rostedt wrote:
>> > On Fri, 2011-06-24 at 17:21 +0800, Yong Zhang wrote:
>> >> Hi,
>> >>
>> >> When I use kprobe to do something, I found some wired thing.
>> >>
>> >> When CONFIG_FUNCTION_TRACER is disabled:
>> >> (gdb) disassemble do_fork
>> >> Dump of assembler code for function do_fork:
>> >>    0xc0037390 <+0>:        mflr    r0
>> >>    0xc0037394 <+4>:        stwu    r1,-64(r1)
>> >>    0xc0037398 <+8>:        mfcr    r12
>> >>    0xc003739c <+12>:       stmw    r27,44(r1)
>> >>
>> >> Then I:
>> >> modprobe kprobe_example func=do_fork offset=4
>> >> ls
>> >> Things works well.
>> >>
>> >> But when CONFIG_FUNCTION_TRACER is enabled:
>> >> (gdb) disassemble do_fork
>> >> Dump of assembler code for function do_fork:
>> >>    0xc0040334 <+0>:        mflr    r0
>> >>    0xc0040338 <+4>:        stw     r0,4(r1)
>> >>    0xc004033c <+8>:        bl      0xc00109d4 <mcount>
>> >>    0xc0040340 <+12>:       stwu    r1,-80(r1)
>> >>    0xc0040344 <+16>:       mflr    r0
>> >>    0xc0040348 <+20>:       stw     r0,84(r1)
>> >>    0xc004034c <+24>:       mfcr    r12
>> >> Then I:
>> >> modprobe kprobe_example func=do_fork offset=12
>> >> ls
>> >> 'ls' will never retrun. system freeze.
>> >
>> > I'm not sure if x86 had a similar issue.
>> >
>> > Masami, have any ideas to why this happened?
>>
>> No, I don't familiar with ppc implementation. I guess
>> that single-step resume code failed to emulate the
>> instruction, but it strongly depends on ppc arch.
>> Maybe IBM people may know what happened.
>>
>> Ananth, Jim, would you have any ideas?
>
> On powerpc, we emulate sstep whenever possible. Only recently support to
> emulate loads and stores got added. I don't have access to a powerpc box
> today... but will try to recreate the problem ASAP and see what could be
> happening in the presence of mcount.

After taking more testing on it, it looks like the issue doesn't
depend on mcount
(AKA. CONFIG_FUNCTION_TRACER)

As I said in the first email, with eldk-5.0 CONFIG_FUNCTION_TRACER=n
will work well.

But when I'm using eldk-4.2[1], both will fail. But the funny thing is when I
set kprobe at several functions some works fine but some will fail. For example,
at this time do_fork() works well, but show_interrupt() will crash.

root at unknown:/root> insmod kprobe_example.ko func=show_interrupts
Planted kprobe at c009be18
root at unknown:/root> cat /proc/interrupts
pre_handler: p->addr = 0xc009be18, nip = 0xc009be18, msr = 0x29000
post_handler: p->addr = 0xc009be18, msr = 0x29000,boostable = 1
Oops: Exception in kernel mode, sig: 11 [#1]
PREEMPT MPC8536 DS
Modules linked in: kprobe_example
NIP: df159e74 LR: c0106f40 CTR: c009be18
REGS: df159d90 TRAP: 0700   Not tainted  (3.0.0-rc4-00001-ge8ffcca-dirty)
MSR: 00029000 <EE,ME,CE>  CR: 20202688  XER: 00000000
TASK = dfaa5340[613] 'cat' THREAD: df158000
GPR00: fffff000 df159e40 dfaa5340 df024a00 df159e78 00000000 df159f20 00000001
GPR08: c10060d0 c009be18 00029000 df159e70 00000000 1001ca74 1ffb5f00 100a01cc
GPR16: 00000000 00000000 00000000 00000000 df024a28 df159f20 00000000 dfbff080
GPR24: 10016000 00001000 df159f20 df159e78 dfbff080 df159e78 df024a00 df159e70
NIP [df159e74] 0xdf159e74
LR [c0106f40] seq_read+0x2a4/0x568
Call Trace:
[df159e40] [00029000] 0x29000 (unreliable)
[df159e74] [00000000]   (null)
Instruction dump:
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
---[ end trace 60026bfc1fe79aed ]---
Segmentation fault

Thanks,
Yong

[1]: http://ftp.denx.de/pub/eldk/4.2/

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